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	$237.39	12.424%	$266.8833	$266.88	$266.90	$266.90
Purchase #2	$42.56	5.846%	$45.0481	$45.05	$45.05	$45.00
Purchase #3	$225.46	3.362%	$233.04	$233.04	$233.05	$233.00
Purchase #4	$114.92	7.200%	$123.1942	$123.19	$123.20	$123.20
Purchase #5	$208.55	5.319%	$219.6428	$219.64	$219.65	$219.60
Purchase #6	$190.73	4.418%	$199.1565	$199.16	$199.15	$199.20
Purchase #7	$78.97	8.652%	$85.8025	$85.80	$85.80	$85.80
7 purchase totals =	$1,098.58		$1,172.7674	$1,172.76	$1,172.80	$1,172.70