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	$86.80	4.663%	$90.8475	$90.85	$90.85	$90.80
Purchase #2	$173.25	13.331%	$196.346	$196.35	$196.35	$196.30
Purchase #3	$133.57	12.844%	$150.7257	$150.73	$150.75	$150.70
Purchase #4	$35.70	9.402%	$39.0565	$39.06	$39.05	$39.10
Purchase #5	$81.77	5.134%	$85.9681	$85.97	$85.95	$86.00
Purchase #6	$39.66	9.220%	$43.3167	$43.32	$43.30	$43.30
Purchase #7	$127.32	6.128%	$135.1222	$135.12	$135.10	$135.10
7 purchase totals =	$678.07		$741.3827	$741.40	$741.35	$741.30