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 $55.35   11.307%   $61.6084   $61.61   $61.60   $61.60  
  Purchase #2 $143.72   3.819%   $149.2087   $149.21   $149.20   $149.20  
  Purchase #3 $61.47   10.453%   $67.8955   $67.90   $67.90   $67.90  
  Purchase #4 $201.35   6.309%   $214.0532   $214.05   $214.05   $214.10  
  Purchase #5 $108.96   7.634%   $117.278   $117.28   $117.30   $117.30  
  Purchase #6 $94.80   8.600%   $102.9528   $102.95   $102.95   $103.00  
  Purchase #7 $55.37   11.686%   $61.8405   $61.84   $61.85   $61.80  
  7 purchase totals = $721.02       $774.8371   $774.84   $774.85   $774.90