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	$32.38	4.680%	$33.8954	$33.90	$33.90	$33.90
Purchase #2	$46.41	10.321%	$51.2	$51.20	$51.20	$51.20
Purchase #3	$83.54	6.389%	$88.8774	$88.88	$88.90	$88.90
Purchase #4	$154.66	7.464%	$166.2038	$166.20	$166.20	$166.20
Purchase #5	$212.30	12.496%	$238.829	$238.83	$238.85	$238.80
Purchase #6	$66.27	10.693%	$73.3563	$73.36	$73.35	$73.40
Purchase #7	$92.27	8.282%	$99.9118	$99.91	$99.90	$99.90
7 purchase totals =	$687.83		$752.2737	$752.28	$752.30	$752.30