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 $53.65   13.642%   $60.9689   $60.97   $60.95   $61.00  
  Purchase #2 $31.87   7.636%   $34.3036   $34.30   $34.30   $34.30  
  Purchase #3 $240.54   9.221%   $262.7202   $262.72   $262.70   $262.70  
  Purchase #4 $26.29   9.837%   $28.8761   $28.88   $28.90   $28.90  
  Purchase #5 $154.87   13.871%   $176.352   $176.35   $176.35   $176.40  
  Purchase #6 $42.71   3.511%   $44.2095   $44.21   $44.20   $44.20  
  Purchase #7 $9.68   8.664%   $10.5187   $10.52   $10.50   $10.50  
  7 purchase totals = $559.61       $617.9490   $617.95   $617.90   $618.00