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	$90.28	9.832%	$99.1563	$99.16	$99.15	$99.20
Purchase #2	$116.54	6.316%	$123.9007	$123.90	$123.90	$123.90
Purchase #3	$151.49	11.685%	$169.1916	$169.19	$169.20	$169.20
Purchase #4	$127.96	7.230%	$137.2115	$137.21	$137.20	$137.20
Purchase #5	$210.36	13.309%	$238.3568	$238.36	$238.35	$238.40
Purchase #6	$150.32	4.230%	$156.6785	$156.68	$156.70	$156.70
Purchase #7	$10.38	3.576%	$10.7512	$10.75	$10.75	$10.80
7 purchase totals =	$857.33		$935.2466	$935.25	$935.25	$935.40