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 $207.44   13.197%   $234.8159   $234.82   $234.80   $234.80  
  Purchase #2 $212.41   11.512%   $236.8626   $236.86   $236.85   $236.90  
  Purchase #3 $55.82   7.341%   $59.9177   $59.92   $59.90   $59.90  
  Purchase #4 $213.54   5.363%   $224.9922   $224.99   $225.00   $225.00  
  Purchase #5 $199.93   6.869%   $213.6632   $213.66   $213.65   $213.70  
  Purchase #6 $233.47   9.374%   $255.3555   $255.36   $255.35   $255.40  
  Purchase #7 $164.92   3.368%   $170.4745   $170.47   $170.45   $170.50  
  7 purchase totals = $1,287.53       $1,396.0816   $1,396.08   $1,396.00   $1,396.20