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 $66.26   6.522%   $70.5815   $70.58   $70.60   $70.60  
  Purchase #2 $157.33   3.196%   $162.3583   $162.36   $162.35   $162.40  
  Purchase #3 $234.40   13.348%   $265.6877   $265.69   $265.70   $265.70  
  Purchase #4 $250.66   5.820%   $265.2484   $265.25   $265.25   $265.20  
  Purchase #5 $24.58   3.716%   $25.4934   $25.49   $25.50   $25.50  
  Purchase #6 $231.52   3.297%   $239.1532   $239.15   $239.15   $239.20  
  Purchase #7 $96.95   6.316%   $103.0734   $103.07   $103.05   $103.10  
  7 purchase totals = $1,061.70       $1,131.5959   $1,131.59   $1,131.60   $1,131.70