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 $55.56   12.444%   $62.4739   $62.47   $62.45   $62.50  
  Purchase #2 $144.48   7.793%   $155.7393   $155.74   $155.75   $155.70  
  Purchase #3 $202.54   7.644%   $218.0222   $218.02   $218.00   $218.00  
  Purchase #4 $151.51   6.258%   $160.9915   $160.99   $161.00   $161.00  
  Purchase #5 $118.38   6.165%   $125.6781   $125.68   $125.70   $125.70  
  Purchase #6 $190.45   6.160%   $202.1817   $202.18   $202.20   $202.20  
  Purchase #7 $53.26   9.319%   $58.2233   $58.22   $58.20   $58.20  
  7 purchase totals = $916.18       $983.3100   $983.30   $983.30   $983.30