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 $211.97   8.261%   $229.4808   $229.48   $229.50   $229.50  
  Purchase #2 $73.93   4.581%   $77.3167   $77.32   $77.30   $77.30  
  Purchase #3 $104.83   12.327%   $117.7524   $117.75   $117.75   $117.80  
  Purchase #4 $163.84   7.181%   $175.6054   $175.61   $175.60   $175.60  
  Purchase #5 $236.73   7.374%   $254.1865   $254.19   $254.20   $254.20  
  Purchase #6 $122.54   5.775%   $129.6167   $129.62   $129.60   $129.60  
  Purchase #7 $130.72   3.698%   $135.554   $135.55   $135.55   $135.60  
  7 purchase totals = $1,044.56       $1,119.5125   $1,119.52   $1,119.50   $1,119.60