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	$124.47	9.728%	$136.5784	$136.58	$136.60	$136.60
Purchase #2	$79.28	12.432%	$89.1361	$89.14	$89.15	$89.10
Purchase #3	$48.36	12.676%	$54.4901	$54.49	$54.50	$54.50
Purchase #4	$33.35	11.326%	$37.1272	$37.13	$37.15	$37.10
Purchase #5	$174.69	4.844%	$183.152	$183.15	$183.15	$183.20
Purchase #6	$30.27	3.608%	$31.3621	$31.36	$31.35	$31.40
Purchase #7	$64.96	9.590%	$71.1897	$71.19	$71.20	$71.20
7 purchase totals =	$555.38		$603.0356	$603.04	$603.10	$603.10