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	$81.53	11.763%	$91.1204	$91.12	$91.10	$91.10
Purchase #2	$78.55	4.666%	$82.2151	$82.22	$82.20	$82.20
Purchase #3	$34.94	7.832%	$37.6765	$37.68	$37.70	$37.70
Purchase #4	$11.98	5.311%	$12.6163	$12.62	$12.60	$12.60
Purchase #5	$238.89	9.163%	$260.7795	$260.78	$260.80	$260.80
Purchase #6	$150.57	11.796%	$168.3312	$168.33	$168.35	$168.30
Purchase #7	$93.53	7.301%	$100.3586	$100.36	$100.35	$100.40
7 purchase totals =	$689.99		$753.0976	$753.11	$753.10	$753.10