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	$243.66	8.437%	$264.2176	$264.22	$264.20	$264.20
Purchase #2	$244.53	5.764%	$258.6247	$258.62	$258.60	$258.60
Purchase #3	$108.35	9.175%	$118.2911	$118.29	$118.30	$118.30
Purchase #4	$82.86	12.173%	$92.9465	$92.95	$92.95	$92.90
Purchase #5	$86.75	4.166%	$90.364	$90.36	$90.35	$90.40
Purchase #6	$67.93	6.221%	$72.1559	$72.16	$72.15	$72.20
Purchase #7	$146.57	11.150%	$162.9126	$162.91	$162.90	$162.90
7 purchase totals =	$980.65		$1,059.5124	$1,059.51	$1,059.45	$1,059.50