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	$163.48	4.818%	$171.3565	$171.36	$171.35	$171.40
Purchase #2	$130.41	10.825%	$144.5269	$144.53	$144.55	$144.50
Purchase #3	$88.31	13.137%	$99.9113	$99.91	$99.90	$99.90
Purchase #4	$16.90	13.845%	$19.2398	$19.24	$19.25	$19.20
Purchase #5	$96.70	4.327%	$100.8842	$100.88	$100.90	$100.90
Purchase #6	$168.99	9.434%	$184.9325	$184.93	$184.95	$184.90
Purchase #7	$250.49	13.335%	$283.8928	$283.89	$283.90	$283.90
7 purchase totals =	$915.28		$1,004.7440	$1,004.74	$1,004.80	$1,004.70