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 $13.73   6.261%   $14.5896   $14.59   $14.60   $14.60  
  Purchase #2 $31.44   6.562%   $33.5031   $33.50   $33.50   $33.50  
  Purchase #3 $61.76   8.450%   $66.9787   $66.98   $67.00   $67.00  
  Purchase #4 $167.95   8.269%   $181.8378   $181.84   $181.85   $181.80  
  Purchase #5 $243.44   4.324%   $253.9663   $253.97   $253.95   $254.00  
  Purchase #6 $73.46   9.239%   $80.247   $80.25   $80.25   $80.20  
  Purchase #7 $49.61   9.387%   $54.2669   $54.27   $54.25   $54.30  
  7 purchase totals = $641.39       $685.3894   $685.40   $685.40   $685.40