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 $41.81   11.849%   $46.7641   $46.76   $46.75   $46.80  
  Purchase #2 $138.76   5.731%   $146.7123   $146.71   $146.70   $146.70  
  Purchase #3 $179.88   7.620%   $193.5869   $193.59   $193.60   $193.60  
  Purchase #4 $147.45   9.126%   $160.9063   $160.91   $160.90   $160.90  
  Purchase #5 $33.38   10.699%   $36.9513   $36.95   $36.95   $37.00  
  Purchase #6 $10.33   11.219%   $11.4889   $11.49   $11.50   $11.50  
  Purchase #7 $16.43   9.208%   $17.9429   $17.94   $17.95   $17.90  
  7 purchase totals = $568.04       $614.3527   $614.35   $614.35   $614.40