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	$236.87	7.541%	$254.7324	$254.73	$254.75	$254.70
Purchase #2	$250.57	9.709%	$274.8978	$274.90	$274.90	$274.90
Purchase #3	$128.58	4.297%	$134.1051	$134.11	$134.10	$134.10
Purchase #4	$151.70	5.561%	$160.136	$160.14	$160.15	$160.10
Purchase #5	$65.83	10.716%	$72.8843	$72.88	$72.90	$72.90
Purchase #6	$70.39	12.135%	$78.9318	$78.93	$78.95	$78.90
Purchase #7	$20.27	7.141%	$21.7175	$21.72	$21.70	$21.70
7 purchase totals =	$924.21		$997.4049	$997.41	$997.45	$997.30