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	$158.82	6.212%	$168.6859	$168.69	$168.70	$168.70
Purchase #2	$18.66	6.405%	$19.8552	$19.86	$19.85	$19.90
Purchase #3	$77.45	12.228%	$86.9206	$86.92	$86.90	$86.90
Purchase #4	$230.99	5.477%	$243.6413	$243.64	$243.65	$243.60
Purchase #5	$55.61	11.244%	$61.8628	$61.86	$61.85	$61.90
Purchase #6	$165.98	8.710%	$180.4369	$180.44	$180.45	$180.40
Purchase #7	$76.82	4.242%	$80.0787	$80.08	$80.10	$80.10
7 purchase totals =	$784.33		$841.4814	$841.49	$841.50	$841.50