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	$66.66	13.860%	$75.8991	$75.90	$75.90	$75.90
Purchase #2	$200.83	11.188%	$223.2989	$223.30	$223.30	$223.30
Purchase #3	$162.92	12.562%	$183.386	$183.39	$183.40	$183.40
Purchase #4	$79.36	4.406%	$82.8566	$82.86	$82.85	$82.90
Purchase #5	$22.79	9.780%	$25.0189	$25.02	$25.00	$25.00
Purchase #6	$29.66	4.676%	$31.0469	$31.05	$31.05	$31.00
Purchase #7	$65.30	3.223%	$67.4046	$67.40	$67.40	$67.40
7 purchase totals =	$627.52		$688.9110	$688.92	$688.90	$688.90