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	$190.65	10.346%	$210.3746	$210.37	$210.35	$210.40
Purchase #2	$106.44	8.343%	$115.3203	$115.32	$115.30	$115.30
Purchase #3	$68.68	4.864%	$72.0206	$72.02	$72.00	$72.00
Purchase #4	$29.52	7.853%	$31.8382	$31.84	$31.85	$31.80
Purchase #5	$104.89	6.142%	$111.3323	$111.33	$111.35	$111.30
Purchase #6	$109.79	4.454%	$114.68	$114.68	$114.70	$114.70
Purchase #7	$136.50	8.720%	$148.4028	$148.40	$148.40	$148.40
7 purchase totals =	$746.47		$803.9688	$803.96	$803.95	$803.90