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 $86.82   8.210%   $93.9479   $93.95   $93.95   $93.90  
  Purchase #2 $201.27   13.112%   $227.6605   $227.66   $227.65   $227.70  
  Purchase #3 $99.95   4.282%   $104.2299   $104.23   $104.25   $104.20  
  Purchase #4 $188.36   4.306%   $196.4708   $196.47   $196.45   $196.50  
  Purchase #5 $200.28   12.347%   $225.0086   $225.01   $225.00   $225.00  
  Purchase #6 $207.73   5.820%   $219.8199   $219.82   $219.80   $219.80  
  Purchase #7 $239.39   5.178%   $251.7856   $251.79   $251.80   $251.80  
  7 purchase totals = $1,223.80       $1,318.9232   $1,318.93   $1,318.90   $1,318.90