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	$167.83	9.281%	$183.4063	$183.41	$183.40	$183.40
Purchase #2	$148.51	12.454%	$167.0054	$167.01	$167.00	$167.00
Purchase #3	$54.89	8.793%	$59.7165	$59.72	$59.70	$59.70
Purchase #4	$74.31	9.279%	$81.2052	$81.21	$81.20	$81.20
Purchase #5	$114.38	12.327%	$128.4796	$128.48	$128.50	$128.50
Purchase #6	$10.91	6.457%	$11.6145	$11.61	$11.60	$11.60
Purchase #7	$76.35	12.766%	$86.0968	$86.10	$86.10	$86.10
7 purchase totals =	$647.18		$717.5243	$717.54	$717.50	$717.50