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	$162.78	3.216%	$168.015	$168.02	$168.00	$168.00
Purchase #2	$126.57	12.799%	$142.7697	$142.77	$142.75	$142.80
Purchase #3	$249.49	3.631%	$258.549	$258.55	$258.55	$258.50
Purchase #4	$223.41	9.364%	$244.3301	$244.33	$244.35	$244.30
Purchase #5	$191.52	10.291%	$211.2293	$211.23	$211.25	$211.20
Purchase #6	$52.75	12.448%	$59.3163	$59.32	$59.30	$59.30
Purchase #7	$14.54	13.471%	$16.4987	$16.50	$16.50	$16.50
7 purchase totals =	$1,021.06		$1,100.7081	$1,100.72	$1,100.70	$1,100.60