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 $44.41   8.851%   $48.3407   $48.34   $48.35   $48.30  
  Purchase #2 $199.54   5.280%   $210.0757   $210.08   $210.10   $210.10  
  Purchase #3 $77.50   13.491%   $87.9555   $87.96   $87.95   $88.00  
  Purchase #4 $182.99   12.501%   $205.8656   $205.87   $205.85   $205.90  
  Purchase #5 $115.95   3.668%   $120.203   $120.20   $120.20   $120.20  
  Purchase #6 $32.77   11.482%   $36.5327   $36.53   $36.55   $36.50  
  Purchase #7 $68.86   6.568%   $73.3827   $73.38   $73.40   $73.40  
  7 purchase totals = $722.02       $782.3559   $782.36   $782.40   $782.40