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 $204.80   3.118%   $211.1857   $211.19   $211.20   $211.20  
  Purchase #2 $88.35   11.188%   $98.2346   $98.23   $98.25   $98.20  
  Purchase #3 $219.53   6.266%   $233.2857   $233.29   $233.30   $233.30  
  Purchase #4 $236.90   9.780%   $260.0688   $260.07   $260.05   $260.10  
  Purchase #5 $209.58   4.791%   $219.621   $219.62   $219.60   $219.60  
  Purchase #6 $225.39   3.579%   $233.4567   $233.46   $233.45   $233.50  
  Purchase #7 $250.88   3.300%   $259.159   $259.16   $259.15   $259.20  
  7 purchase totals = $1,435.43       $1,515.0115   $1,515.02   $1,515.00   $1,515.10