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 $89.32   5.206%   $93.97   $93.97   $93.95   $94.00  
  Purchase #2 $62.74   11.181%   $69.755   $69.76   $69.75   $69.80  
  Purchase #3 $215.32   12.708%   $242.6829   $242.68   $242.70   $242.70  
  Purchase #4 $236.89   8.818%   $257.779   $257.78   $257.80   $257.80  
  Purchase #5 $17.50   5.532%   $18.4681   $18.47   $18.45   $18.50  
  Purchase #6 $40.31   5.864%   $42.6738   $42.67   $42.65   $42.70  
  Purchase #7 $181.94   12.685%   $205.0191   $205.02   $205.00   $205.00  
  7 purchase totals = $844.02       $930.3479   $930.35   $930.30   $930.50