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 $97.68   9.589%   $107.0465   $107.05   $107.05   $107.00  
  Purchase #2 $157.99   8.341%   $171.1679   $171.17   $171.15   $171.20  
  Purchase #3 $33.49   6.323%   $35.6076   $35.61   $35.60   $35.60  
  Purchase #4 $91.43   5.817%   $96.7485   $96.75   $96.75   $96.70  
  Purchase #5 $161.63   10.477%   $178.564   $178.56   $178.55   $178.60  
  Purchase #6 $114.57   6.227%   $121.7043   $121.70   $121.70   $121.70  
  Purchase #7 $152.50   11.605%   $170.1976   $170.20   $170.20   $170.20  
  7 purchase totals = $809.29       $881.0364   $881.04   $881.00   $881.00