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 $83.46   11.400%   $92.9744   $92.97   $92.95   $93.00  
  Purchase #2 $25.35   8.500%   $27.5048   $27.50   $27.50   $27.50  
  Purchase #3 $126.90   5.236%   $133.5445   $133.54   $133.55   $133.50  
  Purchase #4 $245.84   12.188%   $275.803   $275.80   $275.80   $275.80  
  Purchase #5 $51.89   5.834%   $54.9173   $54.92   $54.90   $54.90  
  Purchase #6 $119.51   4.533%   $124.9274   $124.93   $124.95   $124.90  
  Purchase #7 $171.31   7.630%   $184.381   $184.38   $184.40   $184.40  
  7 purchase totals = $824.26       $894.0524   $894.04   $894.05   $894.00