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 $226.58   9.282%   $247.6112   $247.61   $247.60   $247.60  
  Purchase #2 $81.43   12.143%   $91.318   $91.32   $91.30   $91.30  
  Purchase #3 $59.55   11.864%   $66.615   $66.62   $66.60   $66.60  
  Purchase #4 $62.92   4.331%   $65.6451   $65.65   $65.65   $65.60  
  Purchase #5 $51.93   12.278%   $58.306   $58.31   $58.30   $58.30  
  Purchase #6 $187.89   8.407%   $203.6859   $203.69   $203.70   $203.70  
  Purchase #7 $163.67   3.120%   $168.7765   $168.78   $168.80   $168.80  
  7 purchase totals = $833.97       $901.9577   $901.98   $901.95   $901.90