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 $178.55   9.132%   $194.8552   $194.86   $194.85   $194.90  
  Purchase #2 $236.31   7.463%   $253.9458   $253.95   $253.95   $253.90  
  Purchase #3 $118.55   3.758%   $123.0051   $123.01   $123.00   $123.00  
  Purchase #4 $99.50   11.141%   $110.5853   $110.59   $110.60   $110.60  
  Purchase #5 $126.87   8.389%   $137.5131   $137.51   $137.50   $137.50  
  Purchase #6 $173.63   7.871%   $187.2964   $187.30   $187.30   $187.30  
  Purchase #7 $61.95   4.255%   $64.586   $64.59   $64.60   $64.60  
  7 purchase totals = $995.36       $1,071.7869   $1,071.81   $1,071.80   $1,071.80