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 $125.71   6.741%   $134.1841   $134.18   $134.20   $134.20  
  Purchase #2 $61.52   4.316%   $64.1752   $64.18   $64.20   $64.20  
  Purchase #3 $180.84   6.223%   $192.0937   $192.09   $192.10   $192.10  
  Purchase #4 $54.33   3.710%   $56.3456   $56.35   $56.35   $56.30  
  Purchase #5 $232.50   4.659%   $243.3322   $243.33   $243.35   $243.30  
  Purchase #6 $161.54   8.254%   $174.8735   $174.87   $174.85   $174.90  
  Purchase #7 $140.63   13.505%   $159.6221   $159.62   $159.60   $159.60  
  7 purchase totals = $957.07       $1,024.6264   $1,024.62   $1,024.65   $1,024.60