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	$84.29	7.861%	$90.916	$90.92	$90.90	$90.90
Purchase #2	$200.87	11.173%	$223.3132	$223.31	$223.30	$223.30
Purchase #3	$234.33	5.506%	$247.2322	$247.23	$247.25	$247.20
Purchase #4	$35.68	4.152%	$37.1614	$37.16	$37.15	$37.20
Purchase #5	$28.42	12.538%	$31.9833	$31.98	$32.00	$32.00
Purchase #6	$198.77	12.411%	$223.4393	$223.44	$223.45	$223.40
Purchase #7	$28.34	5.163%	$29.8032	$29.80	$29.80	$29.80
7 purchase totals =	$810.70		$883.8486	$883.84	$883.85	$883.80