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 $214.65   11.746%   $239.8628   $239.86   $239.85   $239.90  
  Purchase #2 $166.72   10.540%   $184.2923   $184.29   $184.30   $184.30  
  Purchase #3 $243.41   10.678%   $269.4013   $269.40   $269.40   $269.40  
  Purchase #4 $72.69   11.670%   $81.1729   $81.17   $81.15   $81.20  
  Purchase #5 $178.27   5.627%   $188.3013   $188.30   $188.30   $188.30  
  Purchase #6 $73.80   6.800%   $78.8184   $78.82   $78.80   $78.80  
  Purchase #7 $110.51   6.551%   $117.7495   $117.75   $117.75   $117.70  
  7 purchase totals = $1,060.05       $1,159.5985   $1,159.59   $1,159.55   $1,159.60