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 $218.97   8.614%   $237.8321   $237.83   $237.85   $237.80  
  Purchase #2 $116.39   9.111%   $126.9943   $126.99   $127.00   $127.00  
  Purchase #3 $85.68   10.404%   $94.5941   $94.59   $94.60   $94.60  
  Purchase #4 $250.83   10.645%   $277.5309   $277.53   $277.55   $277.50  
  Purchase #5 $159.28   4.351%   $166.2103   $166.21   $166.20   $166.20  
  Purchase #6 $185.35   6.661%   $197.6962   $197.70   $197.70   $197.70  
  Purchase #7 $103.51   12.777%   $116.7355   $116.74   $116.75   $116.70  
  7 purchase totals = $1,120.01       $1,217.5934   $1,217.59   $1,217.65   $1,217.50