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	$120.37	9.350%	$131.6246	$131.62	$131.60	$131.60
Purchase #2	$156.75	10.545%	$173.2793	$173.28	$173.30	$173.30
Purchase #3	$239.76	4.630%	$250.8609	$250.86	$250.85	$250.90
Purchase #4	$139.51	9.482%	$152.7383	$152.74	$152.75	$152.70
Purchase #5	$217.44	8.451%	$235.8159	$235.82	$235.80	$235.80
Purchase #6	$42.51	10.300%	$46.8885	$46.89	$46.90	$46.90
Purchase #7	$6.55	12.314%	$7.3566	$7.36	$7.35	$7.40
7 purchase totals =	$922.89		$998.5641	$998.57	$998.55	$998.60