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 $94.89   7.713%   $102.2089   $102.21   $102.20   $102.20  
  Purchase #2 $103.65   10.304%   $114.3301   $114.33   $114.35   $114.30  
  Purchase #3 $162.97   6.615%   $173.7505   $173.75   $173.75   $173.80  
  Purchase #4 $247.57   7.374%   $265.8258   $265.83   $265.85   $265.80  
  Purchase #5 $143.32   7.243%   $153.7007   $153.70   $153.70   $153.70  
  Purchase #6 $97.92   3.448%   $101.2963   $101.30   $101.30   $101.30  
  Purchase #7 $224.75   7.576%   $241.7771   $241.78   $241.80   $241.80  
  7 purchase totals = $1,075.07       $1,152.8894   $1,152.90   $1,152.95   $1,152.90