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 $46.82   10.267%   $51.627   $51.63   $51.65   $51.60  
  Purchase #2 $165.87   10.658%   $183.5484   $183.55   $183.55   $183.50  
  Purchase #3 $135.42   3.786%   $140.547   $140.55   $140.55   $140.50  
  Purchase #4 $44.77   13.628%   $50.8713   $50.87   $50.85   $50.90  
  Purchase #5 $87.85   4.696%   $91.9754   $91.98   $92.00   $92.00  
  Purchase #6 $34.37   12.828%   $38.779   $38.78   $38.80   $38.80  
  Purchase #7 $245.31   3.507%   $253.913   $253.91   $253.90   $253.90  
  7 purchase totals = $760.41       $811.2611   $811.27   $811.30   $811.20