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 $156.67   11.162%   $174.1575   $174.16   $174.15   $174.20  
  Purchase #2 $59.39   13.796%   $67.5834   $67.58   $67.60   $67.60  
  Purchase #3 $73.68   4.584%   $77.0575   $77.06   $77.05   $77.10  
  Purchase #4 $212.51   3.337%   $219.6015   $219.60   $219.60   $219.60  
  Purchase #5 $30.68   9.749%   $33.671   $33.67   $33.65   $33.70  
  Purchase #6 $82.63   6.563%   $88.053   $88.05   $88.05   $88.10  
  Purchase #7 $155.61   8.721%   $169.1807   $169.18   $169.20   $169.20  
  7 purchase totals = $771.17       $829.3046   $829.30   $829.30   $829.50