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	$145.59	10.739%	$161.2249	$161.22	$161.20	$161.20
Purchase #2	$174.65	12.745%	$196.9091	$196.91	$196.90	$196.90
Purchase #3	$16.86	4.499%	$17.6185	$17.62	$17.60	$17.60
Purchase #4	$149.71	7.604%	$161.0939	$161.09	$161.10	$161.10
Purchase #5	$216.74	13.113%	$245.1611	$245.16	$245.15	$245.20
Purchase #6	$27.74	12.322%	$31.1581	$31.16	$31.15	$31.20
Purchase #7	$85.46	4.345%	$89.1732	$89.17	$89.15	$89.20
7 purchase totals =	$816.75		$902.3388	$902.33	$902.25	$902.40