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	$220.43	13.843%	$250.9441	$250.94	$250.95	$250.90
Purchase #2	$167.52	10.490%	$185.0928	$185.09	$185.10	$185.10
Purchase #3	$48.98	8.589%	$53.1869	$53.19	$53.20	$53.20
Purchase #4	$79.33	7.341%	$85.1536	$85.15	$85.15	$85.20
Purchase #5	$232.67	7.601%	$250.3552	$250.36	$250.35	$250.40
Purchase #6	$199.60	9.665%	$218.8913	$218.89	$218.90	$218.90
Purchase #7	$115.67	9.603%	$126.7778	$126.78	$126.80	$126.80
7 purchase totals =	$1,064.20		$1,170.4017	$1,170.40	$1,170.45	$1,170.50