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	$89.58	4.841%	$93.9166	$93.92	$93.90	$93.90
Purchase #2	$64.25	11.452%	$71.6079	$71.61	$71.60	$71.60
Purchase #3	$36.64	10.700%	$40.5605	$40.56	$40.55	$40.60
Purchase #4	$104.28	13.474%	$118.3307	$118.33	$118.35	$118.30
Purchase #5	$46.96	13.248%	$53.1813	$53.18	$53.20	$53.20
Purchase #6	$85.66	10.764%	$94.8804	$94.88	$94.90	$94.90
Purchase #7	$71.90	7.746%	$77.4694	$77.47	$77.45	$77.50
7 purchase totals =	$499.27		$549.9468	$549.95	$549.95	$550.00