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 $185.67   6.829%   $198.3494   $198.35   $198.35   $198.30  
  Purchase #2 $200.51   8.198%   $216.9478   $216.95   $216.95   $216.90  
  Purchase #3 $104.96   7.578%   $112.9139   $112.91   $112.90   $112.90  
  Purchase #4 $46.83   5.505%   $49.408   $49.41   $49.40   $49.40  
  Purchase #5 $98.81   3.530%   $102.298   $102.30   $102.30   $102.30  
  Purchase #6 $94.27   11.338%   $104.9583   $104.96   $104.95   $105.00  
  Purchase #7 $246.42   11.499%   $274.7558   $274.76   $274.75   $274.80  
  7 purchase totals = $977.47       $1,059.6312   $1,059.64   $1,059.60   $1,059.60