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	$79.51	11.666%	$88.7856	$88.79	$88.80	$88.80
Purchase #2	$233.59	13.216%	$264.4613	$264.46	$264.45	$264.50
Purchase #3	$136.88	9.520%	$149.911	$149.91	$149.90	$149.90
Purchase #4	$151.55	10.370%	$167.2657	$167.27	$167.25	$167.30
Purchase #5	$74.88	10.553%	$82.7821	$82.78	$82.80	$82.80
Purchase #6	$161.97	11.249%	$180.19	$180.19	$180.20	$180.20
Purchase #7	$46.52	3.423%	$48.1124	$48.11	$48.10	$48.10
7 purchase totals =	$884.90		$981.5081	$981.51	$981.50	$981.60