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 $245.97   4.332%   $256.6254   $256.63   $256.65   $256.60  
  Purchase #2 $44.86   12.191%   $50.3289   $50.33   $50.35   $50.30  
  Purchase #3 $93.42   12.214%   $104.8303   $104.83   $104.85   $104.80  
  Purchase #4 $198.74   7.775%   $214.192   $214.19   $214.20   $214.20  
  Purchase #5 $52.43   10.616%   $57.996   $58.00   $58.00   $58.00  
  Purchase #6 $45.48   4.148%   $47.3665   $47.37   $47.35   $47.40  
  Purchase #7 $221.58   7.280%   $237.711   $237.71   $237.70   $237.70  
  7 purchase totals = $902.48       $969.0501   $969.06   $969.10   $969.00