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 $191.99   8.134%   $207.6065   $207.61   $207.60   $207.60  
  Purchase #2 $233.49   3.114%   $240.7609   $240.76   $240.75   $240.80  
  Purchase #3 $35.82   13.241%   $40.5629   $40.56   $40.55   $40.60  
  Purchase #4 $210.57   10.763%   $233.2336   $233.23   $233.25   $233.20  
  Purchase #5 $25.64   4.234%   $26.7256   $26.73   $26.75   $26.70  
  Purchase #6 $232.97   13.805%   $265.1315   $265.13   $265.15   $265.10  
  Purchase #7 $25.58   6.699%   $27.2936   $27.29   $27.30   $27.30  
  7 purchase totals = $956.06       $1,041.3146   $1,041.31   $1,041.35   $1,041.30