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	$34.41	8.571%	$37.3593	$37.36	$37.35	$37.40
Purchase #2	$93.45	6.230%	$99.2719	$99.27	$99.25	$99.30
Purchase #3	$89.95	7.375%	$96.5838	$96.58	$96.60	$96.60
Purchase #4	$59.25	10.148%	$65.2627	$65.26	$65.25	$65.30
Purchase #5	$227.52	3.237%	$234.8848	$234.88	$234.90	$234.90
Purchase #6	$73.39	10.856%	$81.3572	$81.36	$81.35	$81.40
Purchase #7	$161.96	8.127%	$175.1225	$175.12	$175.10	$175.10
7 purchase totals =	$739.93		$789.8422	$789.83	$789.80	$790.00