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 $167.76   5.834%   $177.5471   $177.55   $177.55   $177.50  
  Purchase #2 $49.36   5.388%   $52.0195   $52.02   $52.00   $52.00  
  Purchase #3 $83.86   13.526%   $95.2029   $95.20   $95.20   $95.20  
  Purchase #4 $27.99   4.762%   $29.3229   $29.32   $29.30   $29.30  
  Purchase #5 $38.62   7.452%   $41.498   $41.50   $41.50   $41.50  
  Purchase #6 $246.74   5.822%   $261.1052   $261.11   $261.10   $261.10  
  Purchase #7 $104.95   10.205%   $115.6601   $115.66   $115.65   $115.70  
  7 purchase totals = $719.28       $772.3557   $772.36   $772.30   $772.30