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	$21.37	8.344%	$23.1531	$23.15	$23.15	$23.20
Purchase #2	$125.54	12.214%	$140.8735	$140.87	$140.85	$140.90
Purchase #3	$36.44	13.289%	$41.2825	$41.28	$41.30	$41.30
Purchase #4	$39.62	13.690%	$45.044	$45.04	$45.05	$45.00
Purchase #5	$62.28	5.799%	$65.8916	$65.89	$65.90	$65.90
Purchase #6	$175.83	5.368%	$185.2686	$185.27	$185.25	$185.30
Purchase #7	$51.58	5.182%	$54.2529	$54.25	$54.25	$54.30
7 purchase totals =	$512.66		$555.7662	$555.75	$555.75	$555.90