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 $182.98   6.488%   $194.8517   $194.85   $194.85   $194.90  
  Purchase #2 $205.37   11.626%   $229.2463   $229.25   $229.25   $229.20  
  Purchase #3 $240.99   4.359%   $251.4948   $251.49   $251.50   $251.50  
  Purchase #4 $236.29   9.698%   $259.2054   $259.21   $259.20   $259.20  
  Purchase #5 $176.59   11.209%   $196.384   $196.38   $196.40   $196.40  
  Purchase #6 $112.39   8.486%   $121.9274   $121.93   $121.95   $121.90  
  Purchase #7 $96.68   6.333%   $102.8027   $102.80   $102.80   $102.80  
  7 purchase totals = $1,251.29       $1,355.9123   $1,355.91   $1,355.95   $1,355.90