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	$84.71	9.254%	$92.5491	$92.55	$92.55	$92.50
Purchase #2	$94.48	11.122%	$104.9881	$104.99	$105.00	$105.00
Purchase #3	$74.94	10.531%	$82.8319	$82.83	$82.85	$82.80
Purchase #4	$38.68	3.668%	$40.0988	$40.10	$40.10	$40.10
Purchase #5	$131.86	12.330%	$148.1183	$148.12	$148.10	$148.10
Purchase #6	$103.89	8.430%	$112.6479	$112.65	$112.65	$112.60
Purchase #7	$199.62	11.745%	$223.0654	$223.07	$223.05	$223.10
7 purchase totals =	$728.18		$804.2995	$804.31	$804.30	$804.20