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 $113.87   10.278%   $125.5736   $125.57   $125.55   $125.60  
  Purchase #2 $211.73   8.833%   $230.4321   $230.43   $230.45   $230.40  
  Purchase #3 $73.57   8.554%   $79.8632   $79.86   $79.85   $79.90  
  Purchase #4 $193.65   5.365%   $204.0393   $204.04   $204.05   $204.00  
  Purchase #5 $89.60   13.113%   $101.3492   $101.35   $101.35   $101.30  
  Purchase #6 $106.60   11.627%   $118.9944   $118.99   $119.00   $119.00  
  Purchase #7 $52.37   6.264%   $55.6505   $55.65   $55.65   $55.70  
  7 purchase totals = $841.39       $915.9023   $915.89   $915.90   $915.90