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 $116.99   13.413%   $132.6819   $132.68   $132.70   $132.70  
  Purchase #2 $196.55   9.492%   $215.2065   $215.21   $215.20   $215.20  
  Purchase #3 $231.26   12.851%   $260.9792   $260.98   $261.00   $261.00  
  Purchase #4 $112.46   6.132%   $119.356   $119.36   $119.35   $119.40  
  Purchase #5 $169.58   11.456%   $189.0071   $189.01   $189.00   $189.00  
  Purchase #6 $155.79   5.413%   $164.2229   $164.22   $164.20   $164.20  
  Purchase #7 $10.61   5.466%   $11.1899   $11.19   $11.20   $11.20  
  7 purchase totals = $993.24       $1,092.6435   $1,092.65   $1,092.65   $1,092.70