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 $60.61   3.152%   $62.5204   $62.52   $62.50   $62.50  
  Purchase #2 $204.54   12.766%   $230.6516   $230.65   $230.65   $230.70  
  Purchase #3 $8.32   13.378%   $9.433   $9.43   $9.45   $9.40  
  Purchase #4 $74.49   9.811%   $81.7982   $81.80   $81.80   $81.80  
  Purchase #5 $153.71   13.258%   $174.0889   $174.09   $174.10   $174.10  
  Purchase #6 $190.56   3.402%   $197.0429   $197.04   $197.05   $197.00  
  Purchase #7 $45.90   5.826%   $48.5741   $48.57   $48.55   $48.60  
  7 purchase totals = $738.13       $804.1091   $804.10   $804.10   $804.10