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 $61.68   5.710%   $65.2019   $65.20   $65.20   $65.20  
  Purchase #2 $11.86   10.130%   $13.0614   $13.06   $13.05   $13.10  
  Purchase #3 $152.87   4.147%   $159.2095   $159.21   $159.20   $159.20  
  Purchase #4 $169.96   3.617%   $176.1075   $176.11   $176.10   $176.10  
  Purchase #5 $22.80   12.734%   $25.7034   $25.70   $25.70   $25.70  
  Purchase #6 $246.50   5.376%   $259.7518   $259.75   $259.75   $259.80  
  Purchase #7 $172.85   7.314%   $185.4922   $185.49   $185.50   $185.50  
  7 purchase totals = $838.52       $884.5277   $884.52   $884.50   $884.60