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	$19.55	7.564%	$21.0288	$21.03	$21.05	$21.00
Purchase #2	$221.87	3.829%	$230.3654	$230.37	$230.35	$230.40
Purchase #3	$94.84	7.873%	$102.3068	$102.31	$102.30	$102.30
Purchase #4	$168.46	10.144%	$185.5486	$185.55	$185.55	$185.50
Purchase #5	$57.85	7.872%	$62.404	$62.40	$62.40	$62.40
Purchase #6	$247.59	10.157%	$272.7377	$272.74	$272.75	$272.70
Purchase #7	$116.38	6.179%	$123.5711	$123.57	$123.55	$123.60
7 purchase totals =	$926.54		$997.9624	$997.97	$997.95	$997.90