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	$38.94	6.659%	$41.533	$41.53	$41.55	$41.50
Purchase #2	$94.27	8.539%	$102.3197	$102.32	$102.30	$102.30
Purchase #3	$127.39	10.305%	$140.5175	$140.52	$140.50	$140.50
Purchase #4	$221.93	9.259%	$242.4785	$242.48	$242.50	$242.50
Purchase #5	$100.28	11.195%	$111.5063	$111.51	$111.50	$111.50
Purchase #6	$152.25	6.427%	$162.0351	$162.04	$162.05	$162.00
Purchase #7	$174.58	3.464%	$180.6275	$180.63	$180.65	$180.60
7 purchase totals =	$909.64		$981.0176	$981.03	$981.05	$980.90