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 $240.80   10.603%   $266.332   $266.33   $266.35   $266.30  
  Purchase #2 $228.45   10.601%   $252.668   $252.67   $252.65   $252.70  
  Purchase #3 $120.57   3.787%   $125.136   $125.14   $125.15   $125.10  
  Purchase #4 $14.39   7.740%   $15.5038   $15.50   $15.50   $15.50  
  Purchase #5 $23.37   5.750%   $24.7138   $24.71   $24.70   $24.70  
  Purchase #6 $35.36   7.752%   $38.1011   $38.10   $38.10   $38.10  
  Purchase #7 $94.54   9.469%   $103.492   $103.49   $103.50   $103.50  
  7 purchase totals = $757.48       $825.9467   $825.94   $825.95   $825.90