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 $221.46   13.503%   $251.3637   $251.36   $251.35   $251.40  
  Purchase #2 $211.97   12.421%   $238.2988   $238.30   $238.30   $238.30  
  Purchase #3 $154.43   5.473%   $162.882   $162.88   $162.90   $162.90  
  Purchase #4 $181.79   10.557%   $200.9816   $200.98   $201.00   $201.00  
  Purchase #5 $168.51   5.746%   $178.1926   $178.19   $178.20   $178.20  
  Purchase #6 $52.71   11.212%   $58.6198   $58.62   $58.60   $58.60  
  Purchase #7 $233.99   9.230%   $255.5873   $255.59   $255.60   $255.60  
  7 purchase totals = $1,224.86       $1,345.9258   $1,345.92   $1,345.95   $1,346.00