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 $158.57   11.412%   $176.666   $176.67   $176.65   $176.70  
  Purchase #2 $88.60   8.314%   $95.9662   $95.97   $95.95   $96.00  
  Purchase #3 $18.40   3.818%   $19.1025   $19.10   $19.10   $19.10  
  Purchase #4 $32.56   13.391%   $36.9201   $36.92   $36.90   $36.90  
  Purchase #5 $216.58   11.838%   $242.2187   $242.22   $242.20   $242.20  
  Purchase #6 $31.28   13.610%   $35.5372   $35.54   $35.55   $35.50  
  Purchase #7 $54.36   11.478%   $60.5994   $60.60   $60.60   $60.60  
  7 purchase totals = $600.35       $667.0101   $667.02   $666.95   $667.00