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 $231.98   9.852%   $254.8347   $254.83   $254.85   $254.80  
  Purchase #2 $240.79   5.755%   $254.6475   $254.65   $254.65   $254.60  
  Purchase #3 $95.26   7.264%   $102.1797   $102.18   $102.20   $102.20  
  Purchase #4 $104.35   4.166%   $108.6972   $108.70   $108.70   $108.70  
  Purchase #5 $248.44   9.604%   $272.3002   $272.30   $272.30   $272.30  
  Purchase #6 $127.46   6.322%   $135.518   $135.52   $135.50   $135.50  
  Purchase #7 $124.55   4.367%   $129.9891   $129.99   $130.00   $130.00  
  7 purchase totals = $1,172.83       $1,258.1664   $1,258.17   $1,258.20   $1,258.10