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	$16.88	12.688%	$19.0217	$19.02	$19.00	$19.00
Purchase #2	$59.97	12.485%	$67.4573	$67.46	$67.45	$67.50
Purchase #3	$110.40	13.551%	$125.3603	$125.36	$125.35	$125.40
Purchase #4	$193.48	7.632%	$208.2464	$208.25	$208.25	$208.20
Purchase #5	$37.58	4.379%	$39.2256	$39.23	$39.25	$39.20
Purchase #6	$83.68	6.417%	$89.0497	$89.05	$89.05	$89.00
Purchase #7	$88.86	12.685%	$100.1319	$100.13	$100.15	$100.10
7 purchase totals =	$590.85		$648.4929	$648.50	$648.50	$648.40