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 $66.99   9.223%   $73.1685   $73.17   $73.15   $73.20  
  Purchase #2 $149.47   7.778%   $161.0958   $161.10   $161.10   $161.10  
  Purchase #3 $46.57   9.251%   $50.8782   $50.88   $50.90   $50.90  
  Purchase #4 $59.64   5.169%   $62.7228   $62.72   $62.70   $62.70  
  Purchase #5 $211.85   13.269%   $239.9604   $239.96   $239.95   $240.00  
  Purchase #6 $184.35   3.290%   $190.4151   $190.42   $190.40   $190.40  
  Purchase #7 $244.29   8.196%   $264.312   $264.31   $264.30   $264.30  
  7 purchase totals = $963.16       $1,042.5528   $1,042.56   $1,042.50   $1,042.60