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 $244.95   9.670%   $268.6367   $268.64   $268.65   $268.60  
  Purchase #2 $53.54   13.453%   $60.7427   $60.74   $60.75   $60.70  
  Purchase #3 $6.37   9.375%   $6.9672   $6.97   $6.95   $7.00  
  Purchase #4 $17.95   13.234%   $20.3255   $20.33   $20.35   $20.30  
  Purchase #5 $52.62   6.463%   $56.0208   $56.02   $56.00   $56.00  
  Purchase #6 $241.75   10.668%   $267.5399   $267.54   $267.55   $267.50  
  Purchase #7 $32.61   10.604%   $36.068   $36.07   $36.05   $36.10  
  7 purchase totals = $649.79       $716.3008   $716.31   $716.30   $716.20