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 $69.35   6.276%   $73.7024   $73.70   $73.70   $73.70  
  Purchase #2 $119.64   10.605%   $132.3278   $132.33   $132.35   $132.30  
  Purchase #3 $213.92   12.508%   $240.6771   $240.68   $240.70   $240.70  
  Purchase #4 $96.33   4.144%   $100.3219   $100.32   $100.30   $100.30  
  Purchase #5 $168.29   11.562%   $187.7477   $187.75   $187.75   $187.70  
  Purchase #6 $106.59   8.669%   $115.8303   $115.83   $115.85   $115.80  
  Purchase #7 $120.63   11.124%   $134.0489   $134.05   $134.05   $134.00  
  7 purchase totals = $894.75       $984.6561   $984.66   $984.70   $984.50