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 $103.67   10.841%   $114.9089   $114.91   $114.90   $114.90  
  Purchase #2 $33.25   4.263%   $34.6674   $34.67   $34.65   $34.70  
  Purchase #3 $226.70   4.151%   $236.1103   $236.11   $236.10   $236.10  
  Purchase #4 $245.96   11.434%   $274.0831   $274.08   $274.10   $274.10  
  Purchase #5 $47.79   5.246%   $50.2971   $50.30   $50.30   $50.30  
  Purchase #6 $203.64   3.479%   $210.7246   $210.72   $210.70   $210.70  
  Purchase #7 $137.26   3.706%   $142.3469   $142.35   $142.35   $142.30  
  7 purchase totals = $998.27       $1,063.1383   $1,063.14   $1,063.10   $1,063.10