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	$35.27	5.828%	$37.3255	$37.33	$37.35	$37.30
Purchase #2	$101.90	9.755%	$111.8403	$111.84	$111.85	$111.80
Purchase #3	$52.45	10.221%	$57.8109	$57.81	$57.80	$57.80
Purchase #4	$139.55	4.145%	$145.3343	$145.33	$145.35	$145.30
Purchase #5	$207.69	10.164%	$228.7996	$228.80	$228.80	$228.80
Purchase #6	$161.33	11.414%	$179.7442	$179.74	$179.75	$179.70
Purchase #7	$110.91	4.751%	$116.1793	$116.18	$116.20	$116.20
7 purchase totals =	$809.10		$877.0341	$877.03	$877.10	$876.90