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	$115.92	10.588%	$128.1936	$128.19	$128.20	$128.20
Purchase #2	$69.73	4.782%	$73.0645	$73.06	$73.05	$73.10
Purchase #3	$81.45	4.564%	$85.1674	$85.17	$85.15	$85.20
Purchase #4	$168.65	9.821%	$185.2131	$185.21	$185.20	$185.20
Purchase #5	$37.87	8.106%	$40.9397	$40.94	$40.95	$40.90
Purchase #6	$192.76	8.515%	$209.1735	$209.17	$209.15	$209.20
Purchase #7	$241.53	6.300%	$256.7464	$256.75	$256.75	$256.70
7 purchase totals =	$907.91		$978.4982	$978.49	$978.45	$978.50