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 $209.97   10.108%   $231.1938   $231.19   $231.20   $231.20  
  Purchase #2 $24.65   12.744%   $27.7914   $27.79   $27.80   $27.80  
  Purchase #3 $58.71   6.793%   $62.6982   $62.70   $62.70   $62.70  
  Purchase #4 $78.83   8.716%   $85.7008   $85.70   $85.70   $85.70  
  Purchase #5 $227.39   8.315%   $246.2975   $246.30   $246.30   $246.30  
  Purchase #6 $227.30   4.661%   $237.8945   $237.89   $237.90   $237.90  
  Purchase #7 $197.60   9.648%   $216.6644   $216.66   $216.65   $216.70  
  7 purchase totals = $1,024.45       $1,108.2406   $1,108.23   $1,108.25   $1,108.30