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 $21.62   11.313%   $24.0659   $24.07   $24.05   $24.10  
  Purchase #2 $118.97   12.624%   $133.9888   $133.99   $134.00   $134.00  
  Purchase #3 $176.64   10.164%   $194.5937   $194.59   $194.60   $194.60  
  Purchase #4 $87.51   9.704%   $96.002   $96.00   $96.00   $96.00  
  Purchase #5 $234.62   13.471%   $266.2257   $266.23   $266.25   $266.20  
  Purchase #6 $16.89   11.415%   $18.818   $18.82   $18.80   $18.80  
  Purchase #7 $38.27   10.394%   $42.2478   $42.25   $42.25   $42.20  
  7 purchase totals = $694.52       $775.9419   $775.95   $775.95   $775.90