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 $63.25   12.258%   $71.0032   $71.00   $71.00   $71.00  
  Purchase #2 $140.28   13.257%   $158.8769   $158.88   $158.90   $158.90  
  Purchase #3 $193.33   7.395%   $207.6268   $207.63   $207.65   $207.60  
  Purchase #4 $90.92   5.854%   $96.2425   $96.24   $96.25   $96.20  
  Purchase #5 $183.59   12.736%   $206.972   $206.97   $206.95   $207.00  
  Purchase #6 $79.43   13.718%   $90.3262   $90.33   $90.35   $90.30  
  Purchase #7 $131.95   6.472%   $140.4898   $140.49   $140.50   $140.50  
  7 purchase totals = $882.75       $971.5374   $971.54   $971.60   $971.50