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 $68.57   8.435%   $74.3539   $74.35   $74.35   $74.40  
  Purchase #2 $188.93   13.519%   $214.4714   $214.47   $214.45   $214.50  
  Purchase #3 $174.50   7.536%   $187.6503   $187.65   $187.65   $187.70  
  Purchase #4 $224.76   11.164%   $249.8522   $249.85   $249.85   $249.90  
  Purchase #5 $22.84   3.118%   $23.5522   $23.55   $23.55   $23.60  
  Purchase #6 $239.76   5.868%   $253.8291   $253.83   $253.85   $253.80  
  Purchase #7 $219.63   11.822%   $245.5947   $245.59   $245.60   $245.60  
  7 purchase totals = $1,138.99       $1,249.3038   $1,249.29   $1,249.30   $1,249.50