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 $56.81   5.193%   $59.7601   $59.76   $59.75   $59.80  
  Purchase #2 $239.72   6.684%   $255.7429   $255.74   $255.75   $255.70  
  Purchase #3 $172.34   4.286%   $179.7265   $179.73   $179.75   $179.70  
  Purchase #4 $194.81   13.257%   $220.636   $220.64   $220.65   $220.60  
  Purchase #5 $169.51   9.102%   $184.9388   $184.94   $184.95   $184.90  
  Purchase #6 $175.51   7.873%   $189.3279   $189.33   $189.35   $189.30  
  Purchase #7 $196.69   9.646%   $215.6627   $215.66   $215.65   $215.70  
  7 purchase totals = $1,205.39       $1,305.7949   $1,305.80   $1,305.85   $1,305.70