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	$154.35	4.301%	$160.9886	$160.99	$161.00	$161.00
Purchase #2	$91.50	8.524%	$99.2995	$99.30	$99.30	$99.30
Purchase #3	$86.85	5.197%	$91.3636	$91.36	$91.35	$91.40
Purchase #4	$166.93	9.426%	$182.6648	$182.66	$182.65	$182.70
Purchase #5	$162.78	6.211%	$172.8903	$172.89	$172.90	$172.90
Purchase #6	$134.85	8.667%	$146.5374	$146.54	$146.55	$146.50
Purchase #7	$83.25	6.690%	$88.8194	$88.82	$88.80	$88.80
7 purchase totals =	$880.51		$942.5636	$942.56	$942.55	$942.60