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 $210.75   11.871%   $235.7681   $235.77   $235.75   $235.80  
  Purchase #2 $195.80   3.486%   $202.6256   $202.63   $202.65   $202.60  
  Purchase #3 $130.85   10.344%   $144.3851   $144.39   $144.40   $144.40  
  Purchase #4 $229.35   10.293%   $252.957   $252.96   $252.95   $253.00  
  Purchase #5 $40.36   13.210%   $45.6916   $45.69   $45.70   $45.70  
  Purchase #6 $189.90   13.339%   $215.2308   $215.23   $215.25   $215.20  
  Purchase #7 $130.73   5.198%   $137.5253   $137.53   $137.55   $137.50  
  7 purchase totals = $1,127.74       $1,234.1835   $1,234.20   $1,234.25   $1,234.20