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 $247.26   8.150%   $267.4117   $267.41   $267.40   $267.40  
  Purchase #2 $35.74   4.585%   $37.3787   $37.38   $37.40   $37.40  
  Purchase #3 $104.32   3.184%   $107.6415   $107.64   $107.65   $107.60  
  Purchase #4 $172.57   5.226%   $181.5885   $181.59   $181.60   $181.60  
  Purchase #5 $116.69   7.617%   $125.5783   $125.58   $125.60   $125.60  
  Purchase #6 $56.47   4.644%   $59.0925   $59.09   $59.10   $59.10  
  Purchase #7 $149.99   4.430%   $156.6346   $156.63   $156.65   $156.60  
  7 purchase totals = $883.04       $935.3258   $935.32   $935.40   $935.30