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 $78.65   6.614%   $83.8519   $83.85   $83.85   $83.90  
  Purchase #2 $235.34   11.598%   $262.6347   $262.63   $262.65   $262.60  
  Purchase #3 $183.77   5.861%   $194.5408   $194.54   $194.55   $194.50  
  Purchase #4 $217.47   12.284%   $244.184   $244.18   $244.20   $244.20  
  Purchase #5 $50.69   13.499%   $57.5326   $57.53   $57.55   $57.50  
  Purchase #6 $51.31   3.210%   $52.9571   $52.96   $52.95   $53.00  
  Purchase #7 $229.57   4.855%   $240.7156   $240.72   $240.70   $240.70  
  7 purchase totals = $1,046.80       $1,136.4167   $1,136.41   $1,136.45   $1,136.40