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	$125.44	8.715%	$136.3721	$136.37	$136.35	$136.40
Purchase #2	$211.70	12.544%	$238.2556	$238.26	$238.25	$238.30
Purchase #3	$223.54	7.562%	$240.4441	$240.44	$240.45	$240.40
Purchase #4	$167.47	10.603%	$185.2268	$185.23	$185.25	$185.20
Purchase #5	$85.76	4.471%	$89.5943	$89.59	$89.60	$89.60
Purchase #6	$140.44	7.779%	$151.3648	$151.36	$151.35	$151.40
Purchase #7	$60.31	13.282%	$68.3204	$68.32	$68.30	$68.30
7 purchase totals =	$1,014.66		$1,109.5781	$1,109.57	$1,109.55	$1,109.60