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 $247.69   10.651%   $274.0715   $274.07   $274.05   $274.10  
  Purchase #2 $215.35   4.755%   $225.5899   $225.59   $225.60   $225.60  
  Purchase #3 $72.73   3.335%   $75.1555   $75.16   $75.15   $75.20  
  Purchase #4 $96.78   13.428%   $109.7756   $109.78   $109.80   $109.80  
  Purchase #5 $226.62   13.685%   $257.6329   $257.63   $257.65   $257.60  
  Purchase #6 $49.69   7.838%   $53.5847   $53.58   $53.60   $53.60  
  Purchase #7 $158.62   5.262%   $166.9666   $166.97   $166.95   $167.00  
  7 purchase totals = $1,067.48       $1,162.7767   $1,162.78   $1,162.80   $1,162.90