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 $128.62   13.117%   $145.4911   $145.49   $145.50   $145.50  
  Purchase #2 $184.82   8.546%   $200.6147   $200.61   $200.60   $200.60  
  Purchase #3 $188.95   7.769%   $203.6295   $203.63   $203.65   $203.60  
  Purchase #4 $140.74   7.600%   $151.4362   $151.44   $151.45   $151.40  
  Purchase #5 $91.68   4.389%   $95.7038   $95.70   $95.70   $95.70  
  Purchase #6 $233.51   8.797%   $254.0519   $254.05   $254.05   $254.10  
  Purchase #7 $23.92   7.429%   $25.697   $25.70   $25.70   $25.70  
  7 purchase totals = $992.24       $1,076.6242   $1,076.62   $1,076.65   $1,076.60