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 $201.50   13.780%   $229.2667   $229.27   $229.25   $229.30  
  Purchase #2 $17.84   5.573%   $18.8342   $18.83   $18.85   $18.80  
  Purchase #3 $197.52   3.482%   $204.3976   $204.40   $204.40   $204.40  
  Purchase #4 $14.29   10.221%   $15.7506   $15.75   $15.75   $15.80  
  Purchase #5 $240.63   5.782%   $254.5432   $254.54   $254.55   $254.50  
  Purchase #6 $59.73   12.605%   $67.259   $67.26   $67.25   $67.30  
  Purchase #7 $158.48   4.541%   $165.6766   $165.68   $165.70   $165.70  
  7 purchase totals = $889.99       $955.7279   $955.73   $955.75   $955.80