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	$78.43	3.801%	$81.4111	$81.41	$81.40	$81.40
Purchase #2	$189.77	6.840%	$202.7503	$202.75	$202.75	$202.80
Purchase #3	$210.73	13.372%	$238.9088	$238.91	$238.90	$238.90
Purchase #4	$236.65	11.492%	$263.8458	$263.85	$263.85	$263.80
Purchase #5	$119.68	6.351%	$127.2809	$127.28	$127.30	$127.30
Purchase #6	$58.98	7.436%	$63.3658	$63.37	$63.35	$63.40
Purchase #7	$159.27	8.781%	$173.2555	$173.26	$173.25	$173.30
7 purchase totals =	$1,053.51		$1,150.8182	$1,150.83	$1,150.80	$1,150.90