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 $85.27   12.404%   $95.8469   $95.85   $95.85   $95.80  
  Purchase #2 $178.64   8.649%   $194.0906   $194.09   $194.10   $194.10  
  Purchase #3 $47.26   10.841%   $52.3835   $52.38   $52.40   $52.40  
  Purchase #4 $149.84   13.408%   $169.9305   $169.93   $169.95   $169.90  
  Purchase #5 $195.73   13.710%   $222.5646   $222.56   $222.55   $222.60  
  Purchase #6 $169.61   13.619%   $192.7092   $192.71   $192.70   $192.70  
  Purchase #7 $140.48   13.490%   $159.4308   $159.43   $159.45   $159.40  
  7 purchase totals = $966.83       $1,086.9561   $1,086.95   $1,087.00   $1,086.90