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 $60.42   8.553%   $65.5877   $65.59   $65.60   $65.60  
  Purchase #2 $145.68   11.299%   $162.1404   $162.14   $162.15   $162.10  
  Purchase #3 $82.48   4.682%   $86.3417   $86.34   $86.35   $86.30  
  Purchase #4 $36.81   6.178%   $39.0841   $39.08   $39.10   $39.10  
  Purchase #5 $180.29   8.635%   $195.858   $195.86   $195.85   $195.90  
  Purchase #6 $186.73   3.638%   $193.5232   $193.52   $193.50   $193.50  
  Purchase #7 $16.53   10.776%   $18.3113   $18.31   $18.30   $18.30  
  7 purchase totals = $708.94       $760.8464   $760.84   $760.85   $760.80