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 $204.55   6.692%   $218.2385   $218.24   $218.25   $218.20  
  Purchase #2 $74.31   13.456%   $84.3092   $84.31   $84.30   $84.30  
  Purchase #3 $106.37   4.723%   $111.3939   $111.39   $111.40   $111.40  
  Purchase #4 $121.56   12.755%   $137.065   $137.07   $137.05   $137.10  
  Purchase #5 $104.98   3.517%   $108.6721   $108.67   $108.65   $108.70  
  Purchase #6 $245.99   3.542%   $254.703   $254.70   $254.70   $254.70  
  Purchase #7 $234.94   11.130%   $261.0888   $261.09   $261.10   $261.10  
  7 purchase totals = $1,092.70       $1,175.4705   $1,175.47   $1,175.45   $1,175.50