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 $68.86   3.788%   $71.4684   $71.47   $71.45   $71.50  
  Purchase #2 $138.39   13.188%   $156.6409   $156.64   $156.65   $156.60  
  Purchase #3 $179.56   4.103%   $186.9273   $186.93   $186.95   $186.90  
  Purchase #4 $158.77   4.609%   $166.0877   $166.09   $166.10   $166.10  
  Purchase #5 $125.29   11.760%   $140.0241   $140.02   $140.00   $140.00  
  Purchase #6 $178.80   4.810%   $187.4003   $187.40   $187.40   $187.40  
  Purchase #7 $19.75   13.151%   $22.3473   $22.35   $22.35   $22.30  
  7 purchase totals = $869.42       $930.8960   $930.90   $930.90   $930.80