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 $234.49   10.785%   $259.7797   $259.78   $259.80   $259.80  
  Purchase #2 $203.41   4.617%   $212.8014   $212.80   $212.80   $212.80  
  Purchase #3 $210.68   13.406%   $238.9238   $238.92   $238.90   $238.90  
  Purchase #4 $110.68   3.575%   $114.6368   $114.64   $114.65   $114.60  
  Purchase #5 $220.29   3.172%   $227.2776   $227.28   $227.30   $227.30  
  Purchase #6 $213.90   5.446%   $225.549   $225.55   $225.55   $225.50  
  Purchase #7 $47.89   13.174%   $54.199   $54.20   $54.20   $54.20  
  7 purchase totals = $1,241.34       $1,333.1673   $1,333.17   $1,333.20   $1,333.10