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	$89.39	11.280%	$99.4732	$99.47	$99.45	$99.50
Purchase #2	$167.64	10.585%	$185.3847	$185.38	$185.40	$185.40
Purchase #3	$156.60	9.217%	$171.0338	$171.03	$171.05	$171.00
Purchase #4	$193.35	9.324%	$211.378	$211.38	$211.40	$211.40
Purchase #5	$27.45	4.165%	$28.5933	$28.59	$28.60	$28.60
Purchase #6	$108.32	13.184%	$122.6009	$122.60	$122.60	$122.60
Purchase #7	$75.69	13.388%	$85.8234	$85.82	$85.80	$85.80
7 purchase totals =	$818.44		$904.2873	$904.27	$904.30	$904.30