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 $56.65   9.414%   $61.983   $61.98   $62.00   $62.00  
  Purchase #2 $121.36   10.291%   $133.8492   $133.85   $133.85   $133.80  
  Purchase #3 $7.32   4.280%   $7.6333   $7.63   $7.65   $7.60  
  Purchase #4 $29.80   9.187%   $32.5377   $32.54   $32.55   $32.50  
  Purchase #5 $207.82   13.706%   $236.3038   $236.30   $236.30   $236.30  
  Purchase #6 $146.31   13.329%   $165.8117   $165.81   $165.80   $165.80  
  Purchase #7 $133.89   4.706%   $140.1909   $140.19   $140.20   $140.20  
  7 purchase totals = $703.15       $778.3096   $778.30   $778.35   $778.20