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 $91.48   8.194%   $98.9759   $98.98   $99.00   $99.00  
  Purchase #2 $21.49   5.678%   $22.7102   $22.71   $22.70   $22.70  
  Purchase #3 $216.81   8.447%   $235.1239   $235.12   $235.10   $235.10  
  Purchase #4 $121.95   8.295%   $132.0658   $132.07   $132.05   $132.10  
  Purchase #5 $65.94   8.474%   $71.5278   $71.53   $71.55   $71.50  
  Purchase #6 $82.72   3.588%   $85.688   $85.69   $85.70   $85.70  
  Purchase #7 $161.51   3.508%   $167.1758   $167.18   $167.20   $167.20  
  7 purchase totals = $761.90       $813.2674   $813.28   $813.30   $813.30