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	$83.49	7.562%	$89.8035	$89.80	$89.80	$89.80
Purchase #2	$246.33	8.780%	$267.9578	$267.96	$267.95	$268.00
Purchase #3	$246.48	11.779%	$275.5129	$275.51	$275.50	$275.50
Purchase #4	$83.87	10.150%	$92.3828	$92.38	$92.40	$92.40
Purchase #5	$183.27	12.869%	$206.855	$206.86	$206.85	$206.90
Purchase #6	$18.91	7.859%	$20.3961	$20.40	$20.40	$20.40
Purchase #7	$23.40	10.194%	$25.7854	$25.79	$25.80	$25.80
7 purchase totals =	$885.75		$978.6935	$978.70	$978.70	$978.80