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	$138.85	5.655%	$146.702	$146.70	$146.70	$146.70
Purchase #2	$81.67	9.354%	$89.3094	$89.31	$89.30	$89.30
Purchase #3	$229.49	9.505%	$251.303	$251.30	$251.30	$251.30
Purchase #4	$152.72	12.796%	$172.2621	$172.26	$172.25	$172.30
Purchase #5	$86.85	9.373%	$94.9905	$94.99	$95.00	$95.00
Purchase #6	$165.64	10.814%	$183.5523	$183.55	$183.55	$183.60
Purchase #7	$152.66	6.280%	$162.247	$162.25	$162.25	$162.20
7 purchase totals =	$1,007.88		$1,100.3663	$1,100.36	$1,100.35	$1,100.40