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 $59.99   3.179%   $61.8971   $61.90   $61.90   $61.90  
  Purchase #2 $217.90   6.327%   $231.6865   $231.69   $231.70   $231.70  
  Purchase #3 $93.47   5.867%   $98.9539   $98.95   $98.95   $99.00  
  Purchase #4 $192.92   7.177%   $206.7659   $206.77   $206.75   $206.80  
  Purchase #5 $177.34   4.644%   $185.5757   $185.58   $185.60   $185.60  
  Purchase #6 $25.41   12.133%   $28.493   $28.49   $28.50   $28.50  
  Purchase #7 $224.52   13.435%   $254.6843   $254.68   $254.70   $254.70  
  7 purchase totals = $991.55       $1,068.0564   $1,068.06   $1,068.10   $1,068.20