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 $113.66   10.455%   $125.5432   $125.54   $125.55   $125.50  
  Purchase #2 $63.57   3.570%   $65.8394   $65.84   $65.85   $65.80  
  Purchase #3 $168.97   4.398%   $176.4013   $176.40   $176.40   $176.40  
  Purchase #4 $37.74   3.791%   $39.1707   $39.17   $39.15   $39.20  
  Purchase #5 $245.61   5.171%   $258.3105   $258.31   $258.30   $258.30  
  Purchase #6 $120.99   3.302%   $124.9851   $124.99   $125.00   $125.00  
  Purchase #7 $194.72   13.504%   $221.015   $221.02   $221.00   $221.00  
  7 purchase totals = $945.26       $1,011.2652   $1,011.27   $1,011.25   $1,011.20