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 $212.74   13.756%   $242.0045   $242.00   $242.00   $242.00  
  Purchase #2 $219.81   6.170%   $233.3723   $233.37   $233.35   $233.40  
  Purchase #3 $10.48   11.390%   $11.6737   $11.67   $11.65   $11.70  
  Purchase #4 $22.45   12.448%   $25.2446   $25.24   $25.25   $25.20  
  Purchase #5 $172.86   10.674%   $191.3111   $191.31   $191.30   $191.30  
  Purchase #6 $158.95   11.566%   $177.3342   $177.33   $177.35   $177.30  
  Purchase #7 $26.93   5.566%   $28.4289   $28.43   $28.45   $28.40  
  7 purchase totals = $824.22       $909.3693   $909.35   $909.35   $909.30