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	$175.86	7.183%	$188.492	$188.49	$188.50	$188.50
Purchase #2	$40.93	11.124%	$45.4831	$45.48	$45.50	$45.50
Purchase #3	$57.73	5.468%	$60.8867	$60.89	$60.90	$60.90
Purchase #4	$168.89	8.641%	$183.4838	$183.48	$183.50	$183.50
Purchase #5	$198.43	12.811%	$223.8509	$223.85	$223.85	$223.90
Purchase #6	$24.90	12.424%	$27.9936	$27.99	$28.00	$28.00
Purchase #7	$20.65	9.120%	$22.5333	$22.53	$22.55	$22.50
7 purchase totals =	$687.39		$752.7234	$752.71	$752.80	$752.80