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 $49.91   11.458%   $55.6287   $55.63   $55.65   $55.60  
  Purchase #2 $226.82   6.840%   $242.3345   $242.33   $242.35   $242.30  
  Purchase #3 $10.31   6.200%   $10.9492   $10.95   $10.95   $10.90  
  Purchase #4 $175.39   5.552%   $185.1277   $185.13   $185.15   $185.10  
  Purchase #5 $201.36   12.306%   $226.1394   $226.14   $226.15   $226.10  
  Purchase #6 $236.61   13.629%   $268.8576   $268.86   $268.85   $268.90  
  Purchase #7 $209.65   4.532%   $219.1513   $219.15   $219.15   $219.20  
  7 purchase totals = $1,110.05       $1,208.1884   $1,208.19   $1,208.25   $1,208.10