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 $147.26   11.844%   $164.7015   $164.70   $164.70   $164.70  
  Purchase #2 $146.63   5.615%   $154.8633   $154.86   $154.85   $154.90  
  Purchase #3 $188.55   13.287%   $213.6026   $213.60   $213.60   $213.60  
  Purchase #4 $157.93   8.102%   $170.7255   $170.73   $170.75   $170.70  
  Purchase #5 $23.49   9.454%   $25.7107   $25.71   $25.70   $25.70  
  Purchase #6 $110.92   11.814%   $124.0241   $124.02   $124.00   $124.00  
  Purchase #7 $186.58   5.814%   $197.4278   $197.43   $197.45   $197.40  
  7 purchase totals = $961.36       $1,051.0555   $1,051.05   $1,051.05   $1,051.00