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 $224.86   8.817%   $244.6859   $244.69   $244.70   $244.70  
  Purchase #2 $221.29   6.800%   $236.3377   $236.34   $236.35   $236.30  
  Purchase #3 $52.78   6.450%   $56.1843   $56.18   $56.20   $56.20  
  Purchase #4 $199.27   9.854%   $218.9061   $218.91   $218.90   $218.90  
  Purchase #5 $187.90   8.759%   $204.3582   $204.36   $204.35   $204.40  
  Purchase #6 $206.31   4.802%   $216.217   $216.22   $216.20   $216.20  
  Purchase #7 $235.43   6.156%   $249.9231   $249.92   $249.90   $249.90  
  7 purchase totals = $1,327.84       $1,426.6123   $1,426.62   $1,426.60   $1,426.60