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	$27.56	4.292%	$28.7429	$28.74	$28.75	$28.70
Purchase #2	$19.85	6.402%	$21.1208	$21.12	$21.10	$21.10
Purchase #3	$69.47	4.306%	$72.4614	$72.46	$72.45	$72.50
Purchase #4	$121.88	8.197%	$131.8705	$131.87	$131.85	$131.90
Purchase #5	$161.62	12.332%	$181.551	$181.55	$181.55	$181.60
Purchase #6	$147.57	6.542%	$157.224	$157.22	$157.20	$157.20
Purchase #7	$13.83	5.265%	$14.5581	$14.56	$14.55	$14.60
7 purchase totals =	$561.78		$607.5287	$607.52	$607.45	$607.60