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 $91.81   4.620%   $96.0516   $96.05   $96.05   $96.10  
  Purchase #2 $228.62   8.380%   $247.7784   $247.78   $247.80   $247.80  
  Purchase #3 $230.35   11.691%   $257.2802   $257.28   $257.30   $257.30  
  Purchase #4 $207.55   9.399%   $227.0576   $227.06   $227.05   $227.10  
  Purchase #5 $198.78   3.202%   $205.1449   $205.14   $205.15   $205.10  
  Purchase #6 $208.43   11.840%   $233.1081   $233.11   $233.10   $233.10  
  Purchase #7 $64.70   13.316%   $73.3155   $73.32   $73.30   $73.30  
  7 purchase totals = $1,230.24       $1,339.7363   $1,339.74   $1,339.75   $1,339.80