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	$178.59	5.469%	$188.3571	$188.36	$188.35	$188.40
Purchase #2	$16.57	8.533%	$17.9839	$17.98	$18.00	$18.00
Purchase #3	$84.89	5.178%	$89.2856	$89.29	$89.30	$89.30
Purchase #4	$91.46	8.460%	$99.1975	$99.20	$99.20	$99.20
Purchase #5	$24.57	12.535%	$27.6498	$27.65	$27.65	$27.60
Purchase #6	$64.41	11.466%	$71.7953	$71.80	$71.80	$71.80
Purchase #7	$146.89	3.120%	$151.473	$151.47	$151.45	$151.50
7 purchase totals =	$607.38		$645.7422	$645.75	$645.75	$645.80