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 $128.63   4.721%   $134.7026   $134.70   $134.70   $134.70  
  Purchase #2 $204.99   5.288%   $215.8299   $215.83   $215.85   $215.80  
  Purchase #3 $234.97   4.324%   $245.1301   $245.13   $245.15   $245.10  
  Purchase #4 $63.47   12.837%   $71.6176   $71.62   $71.60   $71.60  
  Purchase #5 $209.66   4.446%   $218.9815   $218.98   $219.00   $219.00  
  Purchase #6 $219.69   8.219%   $237.7463   $237.75   $237.75   $237.70  
  Purchase #7 $93.34   7.674%   $100.5029   $100.50   $100.50   $100.50  
  7 purchase totals = $1,154.75       $1,224.5109   $1,224.51   $1,224.55   $1,224.40