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 $105.67   4.167%   $110.0733   $110.07   $110.05   $110.10  
  Purchase #2 $109.41   10.701%   $121.118   $121.12   $121.10   $121.10  
  Purchase #3 $49.69   4.830%   $52.09   $52.09   $52.10   $52.10  
  Purchase #4 $148.77   4.206%   $155.0273   $155.03   $155.05   $155.00  
  Purchase #5 $123.63   7.436%   $132.8231   $132.82   $132.80   $132.80  
  Purchase #6 $27.56   9.462%   $30.1677   $30.17   $30.15   $30.20  
  Purchase #7 $105.58   6.401%   $112.3382   $112.34   $112.35   $112.30  
  7 purchase totals = $670.31       $713.6376   $713.64   $713.60   $713.60