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	$147.31	3.107%	$151.8869	$151.89	$151.90	$151.90
Purchase #2	$196.45	10.668%	$217.4073	$217.41	$217.40	$217.40
Purchase #3	$196.60	12.350%	$220.8801	$220.88	$220.90	$220.90
Purchase #4	$136.51	10.444%	$150.7671	$150.77	$150.75	$150.80
Purchase #5	$47.92	11.318%	$53.3436	$53.34	$53.35	$53.30
Purchase #6	$223.48	9.654%	$245.0548	$245.05	$245.05	$245.10
Purchase #7	$227.63	5.673%	$240.5434	$240.54	$240.55	$240.50
7 purchase totals =	$1,175.90		$1,279.8832	$1,279.88	$1,279.90	$1,279.90