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 $88.67   4.275%   $92.4606   $92.46   $92.45   $92.50  
  Purchase #2 $236.33   9.716%   $259.2918   $259.29   $259.30   $259.30  
  Purchase #3 $232.69   7.152%   $249.332   $249.33   $249.35   $249.30  
  Purchase #4 $16.30   4.717%   $17.0689   $17.07   $17.05   $17.10  
  Purchase #5 $179.93   11.208%   $200.0966   $200.10   $200.10   $200.10  
  Purchase #6 $180.89   12.823%   $204.0855   $204.09   $204.10   $204.10  
  Purchase #7 $158.30   13.494%   $179.661   $179.66   $179.65   $179.70  
  7 purchase totals = $1,093.11       $1,201.9964   $1,202.00   $1,202.00   $1,202.10