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 $204.95   8.175%   $221.7047   $221.70   $221.70   $221.70  
  Purchase #2 $53.33   9.113%   $58.19   $58.19   $58.20   $58.20  
  Purchase #3 $113.63   8.721%   $123.5397   $123.54   $123.55   $123.50  
  Purchase #4 $155.94   5.474%   $164.4762   $164.48   $164.50   $164.50  
  Purchase #5 $33.43   9.653%   $36.657   $36.66   $36.65   $36.70  
  Purchase #6 $192.72   7.426%   $207.0314   $207.03   $207.05   $207.00  
  Purchase #7 $74.71   8.349%   $80.9475   $80.95   $80.95   $80.90  
  7 purchase totals = $828.71       $892.5465   $892.55   $892.60   $892.50