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 $235.71   7.313%   $252.9475   $252.95   $252.95   $252.90  
  Purchase #2 $231.87   10.564%   $256.3647   $256.36   $256.35   $256.40  
  Purchase #3 $94.68   10.163%   $104.3023   $104.30   $104.30   $104.30  
  Purchase #4 $50.49   6.434%   $53.7385   $53.74   $53.75   $53.70  
  Purchase #5 $30.76   3.506%   $31.8384   $31.84   $31.85   $31.80  
  Purchase #6 $197.26   5.751%   $208.6044   $208.60   $208.60   $208.60  
  Purchase #7 $212.32   11.475%   $236.6837   $236.68   $236.70   $236.70  
  7 purchase totals = $1,053.09       $1,144.4795   $1,144.47   $1,144.50   $1,144.40