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 $195.81   8.766%   $212.9747   $212.97   $212.95   $213.00  
  Purchase #2 $100.29   10.386%   $110.7061   $110.71   $110.70   $110.70  
  Purchase #3 $70.65   12.145%   $79.2304   $79.23   $79.25   $79.20  
  Purchase #4 $157.81   11.248%   $175.5605   $175.56   $175.55   $175.60  
  Purchase #5 $126.86   5.874%   $134.3118   $134.31   $134.30   $134.30  
  Purchase #6 $216.99   3.349%   $224.257   $224.26   $224.25   $224.30  
  Purchase #7 $28.97   6.848%   $30.9539   $30.95   $30.95   $31.00  
  7 purchase totals = $897.38       $967.9944   $967.99   $967.95   $968.10