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	$96.32	5.773%	$101.8806	$101.88	$101.90	$101.90
Purchase #2	$111.80	11.674%	$124.8515	$124.85	$124.85	$124.90
Purchase #3	$62.97	6.771%	$67.2337	$67.23	$67.25	$67.20
Purchase #4	$244.89	7.835%	$264.0771	$264.08	$264.10	$264.10
Purchase #5	$150.72	6.337%	$160.2711	$160.27	$160.25	$160.30
Purchase #6	$33.54	10.364%	$37.0161	$37.02	$37.00	$37.00
Purchase #7	$140.53	10.811%	$155.7227	$155.72	$155.70	$155.70
7 purchase totals =	$840.77		$911.0528	$911.05	$911.05	$911.10