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	$73.74	4.200%	$76.8371	$76.84	$76.85	$76.80
Purchase #2	$150.32	8.279%	$162.765	$162.77	$162.75	$162.80
Purchase #3	$17.92	5.593%	$18.9223	$18.92	$18.90	$18.90
Purchase #4	$229.49	6.241%	$243.8125	$243.81	$243.80	$243.80
Purchase #5	$193.87	9.307%	$211.9135	$211.91	$211.90	$211.90
Purchase #6	$90.32	9.796%	$99.1677	$99.17	$99.15	$99.20
Purchase #7	$198.56	13.613%	$225.59	$225.59	$225.60	$225.60
7 purchase totals =	$954.22		$1,039.0081	$1,039.01	$1,038.95	$1,039.00