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 $92.40   6.308%   $98.2286   $98.23   $98.25   $98.20  
  Purchase #2 $197.89   5.796%   $209.3597   $209.36   $209.35   $209.40  
  Purchase #3 $119.91   5.263%   $126.2209   $126.22   $126.20   $126.20  
  Purchase #4 $177.36   10.348%   $195.7132   $195.71   $195.70   $195.70  
  Purchase #5 $123.71   4.870%   $129.7347   $129.73   $129.75   $129.70  
  Purchase #6 $212.39   9.285%   $232.1104   $232.11   $232.10   $232.10  
  Purchase #7 $234.42   10.839%   $259.8288   $259.83   $259.85   $259.80  
  7 purchase totals = $1,158.08       $1,251.1963   $1,251.19   $1,251.20   $1,251.10