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 $37.84   8.420%   $41.0261   $41.03   $41.05   $41.00  
  Purchase #2 $111.39   5.870%   $117.9286   $117.93   $117.95   $117.90  
  Purchase #3 $81.35   4.536%   $85.04   $85.04   $85.05   $85.00  
  Purchase #4 $82.62   7.659%   $88.9479   $88.95   $88.95   $88.90  
  Purchase #5 $240.84   11.545%   $268.645   $268.65   $268.65   $268.60  
  Purchase #6 $59.81   11.556%   $66.7216   $66.72   $66.70   $66.70  
  Purchase #7 $181.30   5.385%   $191.063   $191.06   $191.05   $191.10  
  7 purchase totals = $795.15       $859.3722   $859.38   $859.40   $859.20