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 $225.92   5.454%   $238.2417   $238.24   $238.25   $238.20  
  Purchase #2 $78.53   10.687%   $86.9225   $86.92   $86.90   $86.90  
  Purchase #3 $169.29   9.531%   $185.425   $185.43   $185.45   $185.40  
  Purchase #4 $229.29   10.285%   $252.8725   $252.87   $252.85   $252.90  
  Purchase #5 $197.55   8.463%   $214.2687   $214.27   $214.25   $214.30  
  Purchase #6 $75.83   13.345%   $85.9495   $85.95   $85.95   $85.90  
  Purchase #7 $57.71   5.416%   $60.8356   $60.84   $60.85   $60.80  
  7 purchase totals = $1,034.12       $1,124.5155   $1,124.52   $1,124.50   $1,124.40