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 $213.59   8.156%   $231.0104   $231.01   $231.00   $231.00  
  Purchase #2 $113.67   11.589%   $126.8432   $126.84   $126.85   $126.80  
  Purchase #3 $122.39   5.792%   $129.4788   $129.48   $129.50   $129.50  
  Purchase #4 $169.87   3.379%   $175.6099   $175.61   $175.60   $175.60  
  Purchase #5 $235.63   5.241%   $247.9794   $247.98   $248.00   $248.00  
  Purchase #6 $111.39   9.342%   $121.7961   $121.80   $121.80   $121.80  
  Purchase #7 $201.39   7.122%   $215.733   $215.73   $215.75   $215.70  
  7 purchase totals = $1,167.93       $1,248.4508   $1,248.45   $1,248.50   $1,248.40