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	$190.93	12.463%	$214.7256	$214.73	$214.75	$214.70
Purchase #2	$123.73	6.612%	$131.911	$131.91	$131.90	$131.90
Purchase #3	$104.69	13.865%	$119.2053	$119.21	$119.20	$119.20
Purchase #4	$30.37	9.377%	$33.2178	$33.22	$33.20	$33.20
Purchase #5	$14.51	7.459%	$15.5923	$15.59	$15.60	$15.60
Purchase #6	$233.52	8.449%	$253.2501	$253.25	$253.25	$253.30
Purchase #7	$219.34	6.501%	$233.5993	$233.60	$233.60	$233.60
7 purchase totals =	$917.09		$1,001.5014	$1,001.51	$1,001.50	$1,001.50