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 $117.86   4.233%   $122.849   $122.85   $122.85   $122.80  
  Purchase #2 $73.60   3.201%   $75.9559   $75.96   $75.95   $76.00  
  Purchase #3 $45.86   12.529%   $51.6058   $51.61   $51.60   $51.60  
  Purchase #4 $159.56   10.187%   $175.8144   $175.81   $175.80   $175.80  
  Purchase #5 $238.79   5.291%   $251.4244   $251.42   $251.40   $251.40  
  Purchase #6 $22.84   9.136%   $24.9267   $24.93   $24.95   $24.90  
  Purchase #7 $65.33   11.106%   $72.5855   $72.59   $72.60   $72.60  
  7 purchase totals = $723.84       $775.1617   $775.17   $775.15   $775.10