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 $209.69   12.398%   $235.6874   $235.69   $235.70   $235.70  
  Purchase #2 $162.58   9.822%   $178.5486   $178.55   $178.55   $178.50  
  Purchase #3 $191.81   3.169%   $197.8885   $197.89   $197.90   $197.90  
  Purchase #4 $68.77   12.289%   $77.2211   $77.22   $77.20   $77.20  
  Purchase #5 $11.69   5.454%   $12.3276   $12.33   $12.35   $12.30  
  Purchase #6 $165.74   6.429%   $176.3954   $176.40   $176.40   $176.40  
  Purchase #7 $132.41   10.588%   $146.4296   $146.43   $146.45   $146.40  
  7 purchase totals = $942.69       $1,024.4982   $1,024.51   $1,024.55   $1,024.40