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 $104.81   7.420%   $112.5869   $112.59   $112.60   $112.60  
  Purchase #2 $229.48   10.497%   $253.5685   $253.57   $253.55   $253.60  
  Purchase #3 $25.62   5.205%   $26.9535   $26.95   $26.95   $27.00  
  Purchase #4 $57.91   6.769%   $61.8299   $61.83   $61.85   $61.80  
  Purchase #5 $72.56   6.839%   $77.5224   $77.52   $77.50   $77.50  
  Purchase #6 $200.62   3.677%   $207.9968   $208.00   $208.00   $208.00  
  Purchase #7 $164.85   6.402%   $175.4037   $175.40   $175.40   $175.40  
  7 purchase totals = $855.85       $915.8617   $915.86   $915.85   $915.90