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	$142.93	8.685%	$155.3435	$155.34	$155.35	$155.30
Purchase #2	$91.95	12.282%	$103.2433	$103.24	$103.25	$103.20
Purchase #3	$6.33	12.789%	$7.1395	$7.14	$7.15	$7.10
Purchase #4	$227.49	13.612%	$258.4559	$258.46	$258.45	$258.50
Purchase #5	$83.86	7.231%	$89.9239	$89.92	$89.90	$89.90
Purchase #6	$209.43	3.159%	$216.0459	$216.05	$216.05	$216.00
Purchase #7	$85.51	4.107%	$89.0219	$89.02	$89.00	$89.00
7 purchase totals =	$847.50		$919.1739	$919.17	$919.15	$919.00