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 $205.68   12.598%   $231.5916   $231.59   $231.60   $231.60  
  Purchase #2 $166.53   5.536%   $175.7491   $175.75   $175.75   $175.70  
  Purchase #3 $105.89   8.846%   $115.257   $115.26   $115.25   $115.30  
  Purchase #4 $194.74   8.860%   $211.994   $211.99   $212.00   $212.00  
  Purchase #5 $146.88   11.646%   $163.9856   $163.99   $164.00   $164.00  
  Purchase #6 $175.63   13.252%   $198.9045   $198.90   $198.90   $198.90  
  Purchase #7 $133.26   12.198%   $149.5151   $149.52   $149.50   $149.50  
  7 purchase totals = $1,128.61       $1,246.9969   $1,247.00   $1,247.00   $1,247.00