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	$83.54	7.179%	$89.5373	$89.54	$89.55	$89.50
Purchase #2	$139.31	12.205%	$156.3128	$156.31	$156.30	$156.30
Purchase #3	$40.79	5.212%	$42.916	$42.92	$42.90	$42.90
Purchase #4	$144.56	8.165%	$156.3633	$156.36	$156.35	$156.40
Purchase #5	$51.61	4.306%	$53.8323	$53.83	$53.85	$53.80
Purchase #6	$110.88	6.128%	$117.6747	$117.67	$117.65	$117.70
Purchase #7	$229.34	3.150%	$236.5642	$236.56	$236.55	$236.60
7 purchase totals =	$800.03		$853.2006	$853.19	$853.15	$853.20