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	$73.51	13.126%	$83.1589	$83.16	$83.15	$83.20
Purchase #2	$195.27	5.668%	$206.3379	$206.34	$206.35	$206.30
Purchase #3	$111.30	8.600%	$120.8718	$120.87	$120.85	$120.90
Purchase #4	$244.56	12.668%	$275.5409	$275.54	$275.55	$275.50
Purchase #5	$90.56	11.225%	$100.7254	$100.73	$100.75	$100.70
Purchase #6	$155.69	10.226%	$171.6109	$171.61	$171.60	$171.60
Purchase #7	$93.55	4.123%	$97.4071	$97.41	$97.40	$97.40
7 purchase totals =	$964.44		$1,055.6529	$1,055.66	$1,055.65	$1,055.60