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 $84.55   13.807%   $96.2238   $96.22   $96.20   $96.20  
  Purchase #2 $82.31   9.555%   $90.1747   $90.17   $90.15   $90.20  
  Purchase #3 $105.75   8.297%   $114.5241   $114.52   $114.50   $114.50  
  Purchase #4 $240.35   11.153%   $267.1562   $267.16   $267.15   $267.20  
  Purchase #5 $177.71   12.222%   $199.4297   $199.43   $199.45   $199.40  
  Purchase #6 $44.82   8.422%   $48.5947   $48.59   $48.60   $48.60  
  Purchase #7 $140.44   7.482%   $150.9477   $150.95   $150.95   $150.90  
  7 purchase totals = $875.93       $967.0509   $967.04   $967.00   $967.00