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	$81.52	11.282%	$90.7171	$90.72	$90.70	$90.70
Purchase #2	$61.36	9.529%	$67.207	$67.21	$67.20	$67.20
Purchase #3	$151.84	7.173%	$162.7315	$162.73	$162.75	$162.70
Purchase #4	$235.89	6.355%	$250.8808	$250.88	$250.90	$250.90
Purchase #5	$153.31	4.766%	$160.6168	$160.62	$160.60	$160.60
Purchase #6	$13.45	9.119%	$14.6765	$14.68	$14.70	$14.70
Purchase #7	$181.56	3.850%	$188.5501	$188.55	$188.55	$188.60
7 purchase totals =	$878.93		$935.3798	$935.39	$935.40	$935.40