Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $118.72   13.503%   $134.7508   $134.75   $134.75   $134.80  
  Purchase #2 $220.26   11.396%   $245.3608   $245.36   $245.35   $245.40  
  Purchase #3 $149.98   3.470%   $155.1843   $155.18   $155.20   $155.20  
  Purchase #4 $243.99   13.644%   $277.28   $277.28   $277.30   $277.30  
  Purchase #5 $240.98   8.241%   $260.8392   $260.84   $260.85   $260.80  
  Purchase #6 $129.41   12.820%   $146.0004   $146.00   $146.00   $146.00  
  Purchase #7 $197.98   5.687%   $209.2391   $209.24   $209.25   $209.20  
  7 purchase totals = $1,301.32       $1,428.6546   $1,428.65   $1,428.70   $1,428.70