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	$86.61	3.279%	$89.4499	$89.45	$89.45	$89.40
Purchase #2	$105.89	3.104%	$109.1768	$109.18	$109.20	$109.20
Purchase #3	$212.68	6.833%	$227.2124	$227.21	$227.20	$227.20
Purchase #4	$134.85	11.764%	$150.7138	$150.71	$150.70	$150.70
Purchase #5	$122.75	11.824%	$137.264	$137.26	$137.25	$137.30
Purchase #6	$133.65	9.599%	$146.4791	$146.48	$146.50	$146.50
Purchase #7	$91.43	10.485%	$101.0164	$101.02	$101.00	$101.00
7 purchase totals =	$887.86		$961.3124	$961.31	$961.30	$961.30