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	$40.48	4.505%	$42.3036	$42.30	$42.30	$42.30
Purchase #2	$225.96	11.183%	$251.2291	$251.23	$251.25	$251.20
Purchase #3	$66.87	8.254%	$72.3894	$72.39	$72.40	$72.40
Purchase #4	$221.63	12.171%	$248.6046	$248.60	$248.60	$248.60
Purchase #5	$96.88	5.538%	$102.2452	$102.25	$102.25	$102.20
Purchase #6	$155.86	9.126%	$170.0838	$170.08	$170.10	$170.10
Purchase #7	$152.56	13.326%	$172.8901	$172.89	$172.90	$172.90
7 purchase totals =	$960.24		$1,059.7458	$1,059.74	$1,059.80	$1,059.70