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	$94.77	5.836%	$100.3008	$100.30	$100.30	$100.30
Purchase #2	$133.25	7.253%	$142.9146	$142.91	$142.90	$142.90
Purchase #3	$126.80	3.363%	$131.0643	$131.06	$131.05	$131.10
Purchase #4	$235.57	3.299%	$243.3415	$243.34	$243.35	$243.30
Purchase #5	$12.66	7.831%	$13.6514	$13.65	$13.65	$13.70
Purchase #6	$215.74	10.795%	$239.0291	$239.03	$239.05	$239.00
Purchase #7	$212.73	5.195%	$223.7813	$223.78	$223.80	$223.80
7 purchase totals =	$1,031.52		$1,094.0830	$1,094.07	$1,094.10	$1,094.10