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 $245.67   10.555%   $271.6005   $271.60   $271.60   $271.60  
  Purchase #2 $166.99   6.563%   $177.9496   $177.95   $177.95   $177.90  
  Purchase #3 $66.91   7.311%   $71.8018   $71.80   $71.80   $71.80  
  Purchase #4 $184.83   4.733%   $193.578   $193.58   $193.60   $193.60  
  Purchase #5 $199.42   12.435%   $224.2179   $224.22   $224.20   $224.20  
  Purchase #6 $54.80   8.122%   $59.2509   $59.25   $59.25   $59.30  
  Purchase #7 $224.52   10.697%   $248.5369   $248.54   $248.55   $248.50  
  7 purchase totals = $1,143.14       $1,246.9356   $1,246.94   $1,246.95   $1,246.90