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	$67.46	9.104%	$73.6016	$73.60	$73.60	$73.60
Purchase #2	$159.34	5.538%	$168.1642	$168.16	$168.15	$168.20
Purchase #3	$144.36	11.129%	$160.4258	$160.43	$160.45	$160.40
Purchase #4	$178.65	9.735%	$196.0416	$196.04	$196.05	$196.00
Purchase #5	$247.64	9.344%	$270.7795	$270.78	$270.80	$270.80
Purchase #6	$243.71	12.848%	$275.0219	$275.02	$275.00	$275.00
Purchase #7	$192.56	8.416%	$208.7658	$208.77	$208.75	$208.80
7 purchase totals =	$1,233.72		$1,352.8004	$1,352.80	$1,352.80	$1,352.80