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	$26.78	6.821%	$28.6067	$28.61	$28.60	$28.60
Purchase #2	$83.78	9.678%	$91.8882	$91.89	$91.90	$91.90
Purchase #3	$219.81	11.461%	$245.0024	$245.00	$245.00	$245.00
Purchase #4	$233.76	8.380%	$253.3491	$253.35	$253.35	$253.30
Purchase #5	$48.59	10.863%	$53.8683	$53.87	$53.85	$53.90
Purchase #6	$166.73	10.544%	$184.31	$184.31	$184.30	$184.30
Purchase #7	$167.77	12.279%	$188.3705	$188.37	$188.35	$188.40
7 purchase totals =	$947.22		$1,045.3952	$1,045.40	$1,045.35	$1,045.40