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 $119.50   12.556%   $134.5044   $134.50   $134.50   $134.50  
  Purchase #2 $247.28   3.322%   $255.4946   $255.49   $255.50   $255.50  
  Purchase #3 $218.89   10.470%   $241.8078   $241.81   $241.80   $241.80  
  Purchase #4 $61.36   6.843%   $65.5589   $65.56   $65.55   $65.60  
  Purchase #5 $49.58   10.565%   $54.8181   $54.82   $54.80   $54.80  
  Purchase #6 $101.26   6.133%   $107.4703   $107.47   $107.45   $107.50  
  Purchase #7 $154.55   4.808%   $161.9808   $161.98   $162.00   $162.00  
  7 purchase totals = $952.42       $1,021.6349   $1,021.63   $1,021.60   $1,021.70