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 $194.35   12.575%   $218.7895   $218.79   $218.80   $218.80  
  Purchase #2 $174.80   13.872%   $199.0483   $199.05   $199.05   $199.00  
  Purchase #3 $58.55   4.653%   $61.2743   $61.27   $61.25   $61.30  
  Purchase #4 $125.27   6.687%   $133.6468   $133.65   $133.65   $133.60  
  Purchase #5 $191.53   12.159%   $214.8181   $214.82   $214.80   $214.80  
  Purchase #6 $40.81   10.278%   $45.0045   $45.00   $45.00   $45.00  
  Purchase #7 $22.88   6.636%   $24.3983   $24.40   $24.40   $24.40  
  7 purchase totals = $808.19       $896.9798   $896.98   $896.95   $896.90