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 $166.63   9.657%   $182.7215   $182.72   $182.70   $182.70  
  Purchase #2 $5.43   13.747%   $6.1765   $6.18   $6.20   $6.20  
  Purchase #3 $52.91   11.136%   $58.8021   $58.80   $58.80   $58.80  
  Purchase #4 $165.38   3.272%   $170.7912   $170.79   $170.80   $170.80  
  Purchase #5 $191.88   3.177%   $197.976   $197.98   $198.00   $198.00  
  Purchase #6 $232.76   6.410%   $247.6799   $247.68   $247.70   $247.70  
  Purchase #7 $8.97   3.701%   $9.302   $9.30   $9.30   $9.30  
  7 purchase totals = $823.96       $873.4492   $873.45   $873.50   $873.50