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 $211.77   9.197%   $231.2465   $231.25   $231.25   $231.20  
  Purchase #2 $56.78   13.869%   $64.6548   $64.65   $64.65   $64.70  
  Purchase #3 $96.25   7.242%   $103.2204   $103.22   $103.20   $103.20  
  Purchase #4 $216.66   4.286%   $225.946   $225.95   $225.95   $225.90  
  Purchase #5 $33.84   7.347%   $36.3262   $36.33   $36.35   $36.30  
  Purchase #6 $109.95   9.186%   $120.05   $120.05   $120.05   $120.10  
  Purchase #7 $117.67   5.777%   $124.4678   $124.47   $124.45   $124.50  
  7 purchase totals = $842.92       $905.9117   $905.92   $905.90   $905.90