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	$40.98	4.466%	$42.8102	$42.81	$42.80	$42.80
Purchase #2	$201.62	7.511%	$216.7637	$216.76	$216.75	$216.80
Purchase #3	$174.71	7.414%	$187.663	$187.66	$187.65	$187.70
Purchase #4	$147.36	11.534%	$164.3565	$164.36	$164.35	$164.40
Purchase #5	$250.96	10.867%	$278.2318	$278.23	$278.25	$278.20
Purchase #6	$47.82	4.283%	$49.8681	$49.87	$49.85	$49.90
Purchase #7	$131.71	7.645%	$141.7792	$141.78	$141.80	$141.80
7 purchase totals =	$995.16		$1,081.4725	$1,081.47	$1,081.45	$1,081.60