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 $131.55   13.868%   $149.7934   $149.79   $149.80   $149.80  
  Purchase #2 $207.95   12.486%   $233.9146   $233.91   $233.90   $233.90  
  Purchase #3 $59.33   7.851%   $63.988   $63.99   $64.00   $64.00  
  Purchase #4 $61.52   8.620%   $66.823   $66.82   $66.80   $66.80  
  Purchase #5 $220.27   7.188%   $236.103   $236.10   $236.10   $236.10  
  Purchase #6 $56.95   12.723%   $64.1957   $64.20   $64.20   $64.20  
  Purchase #7 $124.73   13.738%   $141.8654   $141.87   $141.85   $141.90  
  7 purchase totals = $862.30       $956.6831   $956.68   $956.65   $956.70