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	$142.76	5.672%	$150.8573	$150.86	$150.85	$150.90
Purchase #2	$221.71	8.637%	$240.8591	$240.86	$240.85	$240.90
Purchase #3	$73.54	4.358%	$76.7449	$76.74	$76.75	$76.70
Purchase #4	$14.79	4.244%	$15.4177	$15.42	$15.40	$15.40
Purchase #5	$44.32	9.121%	$48.3624	$48.36	$48.35	$48.40
Purchase #6	$78.71	13.278%	$89.1611	$89.16	$89.15	$89.20
Purchase #7	$40.46	4.731%	$42.3742	$42.37	$42.35	$42.40
7 purchase totals =	$616.29		$663.7767	$663.77	$663.70	$663.90