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 $60.32   9.602%   $66.1119   $66.11   $66.10   $66.10  
  Purchase #2 $5.95   11.506%   $6.6346   $6.63   $6.65   $6.60  
  Purchase #3 $84.66   9.394%   $92.613   $92.61   $92.60   $92.60  
  Purchase #4 $179.55   13.719%   $204.1825   $204.18   $204.20   $204.20  
  Purchase #5 $113.71   6.638%   $121.2581   $121.26   $121.25   $121.30  
  Purchase #6 $134.27   5.804%   $142.063   $142.06   $142.05   $142.10  
  Purchase #7 $133.80   6.147%   $142.0247   $142.02   $142.00   $142.00  
  7 purchase totals = $712.26       $774.8878   $774.87   $774.85   $774.90