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 $250.68   10.381%   $276.7031   $276.70   $276.70   $276.70  
  Purchase #2 $228.92   6.599%   $244.0264   $244.03   $244.05   $244.00  
  Purchase #3 $201.88   7.743%   $217.5116   $217.51   $217.50   $217.50  
  Purchase #4 $81.46   13.382%   $92.361   $92.36   $92.35   $92.40  
  Purchase #5 $137.57   4.689%   $144.0207   $144.02   $144.00   $144.00  
  Purchase #6 $63.57   6.226%   $67.5279   $67.53   $67.55   $67.50  
  Purchase #7 $120.97   11.800%   $135.2445   $135.24   $135.25   $135.20  
  7 purchase totals = $1,085.05       $1,177.3952   $1,177.39   $1,177.40   $1,177.30