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 $239.50   9.213%   $261.5651   $261.57   $261.55   $261.60  
  Purchase #2 $135.94   4.721%   $142.3577   $142.36   $142.35   $142.40  
  Purchase #3 $68.45   12.666%   $77.1199   $77.12   $77.10   $77.10  
  Purchase #4 $124.88   6.862%   $133.4493   $133.45   $133.45   $133.40  
  Purchase #5 $243.87   13.492%   $276.7729   $276.77   $276.75   $276.80  
  Purchase #6 $106.96   5.460%   $112.8   $112.80   $112.80   $112.80  
  Purchase #7 $214.33   12.425%   $240.9605   $240.96   $240.95   $241.00  
  7 purchase totals = $1,133.93       $1,245.0254   $1,245.03   $1,244.95   $1,245.10