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 $65.74   12.233%   $73.782   $73.78   $73.80   $73.80  
  Purchase #2 $195.43   6.442%   $208.0196   $208.02   $208.00   $208.00  
  Purchase #3 $194.38   7.609%   $209.1704   $209.17   $209.15   $209.20  
  Purchase #4 $220.59   6.783%   $235.5526   $235.55   $235.55   $235.60  
  Purchase #5 $69.90   6.121%   $74.1786   $74.18   $74.20   $74.20  
  Purchase #6 $19.57   8.361%   $21.2062   $21.21   $21.20   $21.20  
  Purchase #7 $191.38   13.521%   $217.2565   $217.26   $217.25   $217.30  
  7 purchase totals = $956.99       $1,039.1659   $1,039.17   $1,039.15   $1,039.30