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 $183.47   10.242%   $202.261   $202.26   $202.25   $202.30  
  Purchase #2 $84.60   6.387%   $90.0034   $90.00   $90.00   $90.00  
  Purchase #3 $183.62   10.702%   $203.271   $203.27   $203.25   $203.30  
  Purchase #4 $43.56   6.726%   $46.4898   $46.49   $46.50   $46.50  
  Purchase #5 $232.30   6.733%   $247.9408   $247.94   $247.95   $247.90  
  Purchase #6 $108.75   9.773%   $119.3781   $119.38   $119.40   $119.40  
  Purchase #7 $241.77   10.270%   $266.5998   $266.60   $266.60   $266.60  
  7 purchase totals = $1,078.07       $1,175.9439   $1,175.94   $1,175.95   $1,176.00