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	$83.85	8.324%	$90.8297	$90.83	$90.85	$90.80
Purchase #2	$74.34	13.696%	$84.5216	$84.52	$84.50	$84.50
Purchase #3	$117.62	11.685%	$131.3639	$131.36	$131.35	$131.40
Purchase #4	$125.56	7.308%	$134.7359	$134.74	$134.75	$134.70
Purchase #5	$139.46	5.867%	$147.6421	$147.64	$147.65	$147.60
Purchase #6	$250.56	12.481%	$281.8324	$281.83	$281.85	$281.80
Purchase #7	$203.41	5.667%	$214.9372	$214.94	$214.95	$214.90
7 purchase totals =	$994.80		$1,085.8628	$1,085.86	$1,085.90	$1,085.70