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 $162.83   11.624%   $181.7574   $181.76   $181.75   $181.80  
  Purchase #2 $231.62   6.624%   $246.9625   $246.96   $246.95   $247.00  
  Purchase #3 $41.55   3.815%   $43.1351   $43.14   $43.15   $43.10  
  Purchase #4 $114.96   3.712%   $119.2273   $119.23   $119.25   $119.20  
  Purchase #5 $65.72   8.760%   $71.4771   $71.48   $71.50   $71.50  
  Purchase #6 $113.29   11.366%   $126.1665   $126.17   $126.15   $126.20  
  Purchase #7 $164.65   3.838%   $170.9693   $170.97   $170.95   $171.00  
  7 purchase totals = $894.62       $959.6952   $959.71   $959.70   $959.80