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	$17.94	10.820%	$19.8811	$19.88	$19.90	$19.90
Purchase #2	$196.59	13.457%	$223.0451	$223.05	$223.05	$223.00
Purchase #3	$211.34	5.503%	$222.97	$222.97	$222.95	$223.00
Purchase #4	$245.39	10.156%	$270.3118	$270.31	$270.30	$270.30
Purchase #5	$114.62	3.285%	$118.3853	$118.39	$118.40	$118.40
Purchase #6	$93.70	6.434%	$99.7287	$99.73	$99.75	$99.70
Purchase #7	$79.98	4.873%	$83.8774	$83.88	$83.90	$83.90
7 purchase totals =	$959.56		$1,038.1994	$1,038.21	$1,038.25	$1,038.20