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 $183.83   11.839%   $205.5936   $205.59   $205.60   $205.60  
  Purchase #2 $250.97   12.310%   $281.8644   $281.86   $281.85   $281.90  
  Purchase #3 $103.61   6.185%   $110.0183   $110.02   $110.00   $110.00  
  Purchase #4 $97.96   4.839%   $102.7003   $102.70   $102.70   $102.70  
  Purchase #5 $32.32   11.109%   $35.9104   $35.91   $35.90   $35.90  
  Purchase #6 $114.37   10.691%   $126.5973   $126.60   $126.60   $126.60  
  Purchase #7 $217.95   10.733%   $241.3426   $241.34   $241.35   $241.30  
  7 purchase totals = $1,001.01       $1,104.0269   $1,104.02   $1,104.00   $1,104.00