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	$18.70	5.431%	$19.7156	$19.72	$19.70	$19.70
Purchase #2	$36.98	13.653%	$42.0289	$42.03	$42.05	$42.00
Purchase #3	$6.41	13.443%	$7.2717	$7.27	$7.25	$7.30
Purchase #4	$68.76	3.731%	$71.3254	$71.33	$71.35	$71.30
Purchase #5	$110.39	5.468%	$116.4261	$116.43	$116.45	$116.40
Purchase #6	$130.37	10.242%	$143.7225	$143.72	$143.70	$143.70
Purchase #7	$28.98	9.799%	$31.8198	$31.82	$31.80	$31.80
7 purchase totals =	$400.59		$432.3100	$432.32	$432.30	$432.20