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	$81.84	8.850%	$89.0828	$89.08	$89.10	$89.10
Purchase #2	$37.94	12.308%	$42.6097	$42.61	$42.60	$42.60
Purchase #3	$197.96	9.381%	$216.5306	$216.53	$216.55	$216.50
Purchase #4	$72.56	5.121%	$76.2758	$76.28	$76.30	$76.30
Purchase #5	$195.73	11.157%	$217.5676	$217.57	$217.55	$217.60
Purchase #6	$225.99	13.556%	$256.6252	$256.63	$256.65	$256.60
Purchase #7	$237.76	4.613%	$248.7279	$248.73	$248.75	$248.70
7 purchase totals =	$1,049.78		$1,147.4196	$1,147.43	$1,147.50	$1,147.40