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 $42.30   5.302%   $44.5427   $44.54   $44.55   $44.50  
  Purchase #2 $241.46   10.162%   $265.9972   $266.00   $266.00   $266.00  
  Purchase #3 $166.67   3.203%   $172.0084   $172.01   $172.00   $172.00  
  Purchase #4 $82.98   5.322%   $87.3962   $87.40   $87.40   $87.40  
  Purchase #5 $40.54   3.797%   $42.0793   $42.08   $42.10   $42.10  
  Purchase #6 $143.83   13.743%   $163.5966   $163.60   $163.60   $163.60  
  Purchase #7 $231.34   9.253%   $252.7459   $252.75   $252.75   $252.70  
  7 purchase totals = $949.12       $1,028.3663   $1,028.38   $1,028.40   $1,028.30