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	$56.28	8.110%	$60.8443	$60.84	$60.85	$60.80
Purchase #2	$232.73	9.637%	$255.1582	$255.16	$255.15	$255.20
Purchase #3	$125.31	4.496%	$130.9439	$130.94	$130.95	$130.90
Purchase #4	$179.46	9.397%	$196.3239	$196.32	$196.30	$196.30
Purchase #5	$188.76	6.113%	$200.2989	$200.30	$200.30	$200.30
Purchase #6	$204.54	3.720%	$212.1489	$212.15	$212.15	$212.10
Purchase #7	$222.56	9.554%	$243.8234	$243.82	$243.80	$243.80
7 purchase totals =	$1,209.64		$1,299.5415	$1,299.53	$1,299.50	$1,299.40