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 $241.25   3.192%   $248.9507   $248.95   $248.95   $249.00  
  Purchase #2 $163.40   13.227%   $185.0129   $185.01   $185.00   $185.00  
  Purchase #3 $104.34   11.247%   $116.0751   $116.08   $116.10   $116.10  
  Purchase #4 $145.36   11.443%   $161.9935   $161.99   $162.00   $162.00  
  Purchase #5 $146.35   3.320%   $151.2088   $151.21   $151.20   $151.20  
  Purchase #6 $173.60   6.428%   $184.759   $184.76   $184.75   $184.80  
  Purchase #7 $146.89   3.239%   $151.6478   $151.65   $151.65   $151.60  
  7 purchase totals = $1,121.19       $1,199.6478   $1,199.65   $1,199.65   $1,199.70