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 $41.76   7.114%   $44.7308   $44.73   $44.75   $44.70  
  Purchase #2 $160.57   12.708%   $180.9752   $180.98   $181.00   $181.00  
  Purchase #3 $156.58   9.330%   $171.1889   $171.19   $171.20   $171.20  
  Purchase #4 $242.39   12.864%   $273.571   $273.57   $273.55   $273.60  
  Purchase #5 $194.56   7.155%   $208.4808   $208.48   $208.50   $208.50  
  Purchase #6 $220.29   7.736%   $237.3316   $237.33   $237.35   $237.30  
  Purchase #7 $133.99   12.733%   $151.0509   $151.05   $151.05   $151.10  
  7 purchase totals = $1,150.14       $1,267.3292   $1,267.33   $1,267.40   $1,267.40