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	$186.91	12.736%	$210.7149	$210.71	$210.70	$210.70
Purchase #2	$36.36	13.168%	$41.1479	$41.15	$41.15	$41.10
Purchase #3	$247.44	13.122%	$279.9091	$279.91	$279.90	$279.90
Purchase #4	$157.39	9.204%	$171.8762	$171.88	$171.90	$171.90
Purchase #5	$63.92	10.370%	$70.5485	$70.55	$70.55	$70.50
Purchase #6	$238.78	12.423%	$268.4436	$268.44	$268.45	$268.40
Purchase #7	$51.27	12.615%	$57.7377	$57.74	$57.75	$57.70
7 purchase totals =	$982.07		$1,100.3779	$1,100.38	$1,100.40	$1,100.20