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	$28.80	11.598%	$32.1402	$32.14	$32.15	$32.10
Purchase #2	$35.93	3.140%	$37.0582	$37.06	$37.05	$37.10
Purchase #3	$192.42	8.649%	$209.0624	$209.06	$209.05	$209.10
Purchase #4	$136.80	13.600%	$155.4048	$155.40	$155.40	$155.40
Purchase #5	$36.30	11.394%	$40.436	$40.44	$40.45	$40.40
Purchase #6	$69.37	7.355%	$74.4722	$74.47	$74.45	$74.50
Purchase #7	$72.72	6.397%	$77.3719	$77.37	$77.35	$77.40
7 purchase totals =	$572.34		$625.9457	$625.94	$625.90	$626.00