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 $74.83   11.600%   $83.5103   $83.51   $83.50   $83.50  
  Purchase #2 $214.28   12.648%   $241.3821   $241.38   $241.40   $241.40  
  Purchase #3 $138.39   12.728%   $156.0043   $156.00   $156.00   $156.00  
  Purchase #4 $112.25   3.826%   $116.5447   $116.54   $116.55   $116.50  
  Purchase #5 $225.51   9.243%   $246.3539   $246.35   $246.35   $246.40  
  Purchase #6 $17.73   6.514%   $18.8849   $18.88   $18.90   $18.90  
  Purchase #7 $113.72   5.121%   $119.5436   $119.54   $119.55   $119.50  
  7 purchase totals = $896.71       $982.2238   $982.20   $982.25   $982.20