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	$179.48	4.358%	$187.3017	$187.30	$187.30	$187.30
Purchase #2	$86.59	11.394%	$96.4561	$96.46	$96.45	$96.50
Purchase #3	$131.33	8.564%	$142.5771	$142.58	$142.60	$142.60
Purchase #4	$79.78	13.165%	$90.283	$90.28	$90.30	$90.30
Purchase #5	$148.26	8.263%	$160.5107	$160.51	$160.50	$160.50
Purchase #6	$232.74	5.388%	$245.28	$245.28	$245.30	$245.30
Purchase #7	$130.63	10.547%	$144.4075	$144.41	$144.40	$144.40
7 purchase totals =	$988.81		$1,066.8161	$1,066.82	$1,066.85	$1,066.90