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 $65.37   12.534%   $73.5635   $73.56   $73.55   $73.60  
  Purchase #2 $100.33   9.823%   $110.1854   $110.19   $110.20   $110.20  
  Purchase #3 $188.62   13.500%   $214.0837   $214.08   $214.10   $214.10  
  Purchase #4 $38.76   3.857%   $40.255   $40.26   $40.25   $40.30  
  Purchase #5 $127.58   4.551%   $133.3862   $133.39   $133.40   $133.40  
  Purchase #6 $131.58   6.642%   $140.3195   $140.32   $140.30   $140.30  
  Purchase #7 $218.57   7.479%   $234.9169   $234.92   $234.90   $234.90  
  7 purchase totals = $870.81       $946.7102   $946.72   $946.70   $946.80