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 $57.53   11.120%   $63.9273   $63.93   $63.95   $63.90  
  Purchase #2 $163.71   11.433%   $182.427   $182.43   $182.45   $182.40  
  Purchase #3 $81.90   4.602%   $85.669   $85.67   $85.65   $85.70  
  Purchase #4 $12.42   8.835%   $13.5173   $13.52   $13.50   $13.50  
  Purchase #5 $50.84   13.234%   $57.5682   $57.57   $57.55   $57.60  
  Purchase #6 $46.69   13.522%   $53.0034   $53.00   $53.00   $53.00  
  Purchase #7 $129.39   13.777%   $147.2161   $147.22   $147.20   $147.20  
  7 purchase totals = $542.48       $603.3283   $603.34   $603.30   $603.30