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	$165.99	7.302%	$178.1106	$178.11	$178.10	$178.10
Purchase #2	$155.63	9.545%	$170.4849	$170.48	$170.50	$170.50
Purchase #3	$72.57	7.654%	$78.1245	$78.12	$78.10	$78.10
Purchase #4	$157.92	12.750%	$178.0548	$178.05	$178.05	$178.10
Purchase #5	$227.37	3.346%	$234.9778	$234.98	$235.00	$235.00
Purchase #6	$153.73	11.643%	$171.6288	$171.63	$171.65	$171.60
Purchase #7	$80.25	12.779%	$90.5051	$90.51	$90.50	$90.50
7 purchase totals =	$1,013.46		$1,101.8865	$1,101.88	$1,101.90	$1,101.90