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 $61.82   10.363%   $68.2264   $68.23   $68.25   $68.20  
  Purchase #2 $189.77   7.631%   $204.2513   $204.25   $204.25   $204.30  
  Purchase #3 $84.56   13.330%   $95.8318   $95.83   $95.85   $95.80  
  Purchase #4 $126.45   9.311%   $138.2238   $138.22   $138.20   $138.20  
  Purchase #5 $128.93   9.736%   $141.4826   $141.48   $141.50   $141.50  
  Purchase #6 $87.70   9.264%   $95.8245   $95.82   $95.80   $95.80  
  Purchase #7 $18.26   9.135%   $19.9281   $19.93   $19.95   $19.90  
  7 purchase totals = $697.49       $763.7685   $763.76   $763.80   $763.70