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	$20.54	3.424%	$21.2433	$21.24	$21.25	$21.20
Purchase #2	$132.68	13.370%	$150.4193	$150.42	$150.40	$150.40
Purchase #3	$111.43	7.276%	$119.5376	$119.54	$119.55	$119.50
Purchase #4	$228.75	11.802%	$255.7471	$255.75	$255.75	$255.70
Purchase #5	$240.28	9.865%	$263.9836	$263.98	$264.00	$264.00
Purchase #6	$80.38	13.302%	$91.0721	$91.07	$91.05	$91.10
Purchase #7	$111.41	7.728%	$120.0198	$120.02	$120.00	$120.00
7 purchase totals =	$925.47		$1,022.0228	$1,022.02	$1,022.00	$1,021.90