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 $57.56   12.266%   $64.6203   $64.62   $64.60   $64.60  
  Purchase #2 $179.67   9.491%   $196.7225   $196.72   $196.70   $196.70  
  Purchase #3 $147.38   13.593%   $167.4134   $167.41   $167.40   $167.40  
  Purchase #4 $137.65   13.318%   $155.9822   $155.98   $156.00   $156.00  
  Purchase #5 $138.71   7.596%   $149.2464   $149.25   $149.25   $149.20  
  Purchase #6 $221.55   11.302%   $246.5896   $246.59   $246.60   $246.60  
  Purchase #7 $65.69   13.703%   $74.6915   $74.69   $74.70   $74.70  
  7 purchase totals = $948.21       $1,055.2659   $1,055.26   $1,055.25   $1,055.20