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	$240.65	7.400%	$258.4581	$258.46	$258.45	$258.50
Purchase #2	$29.99	11.341%	$33.3912	$33.39	$33.40	$33.40
Purchase #3	$46.92	8.219%	$50.7764	$50.78	$50.80	$50.80
Purchase #4	$72.69	13.587%	$82.5664	$82.57	$82.55	$82.60
Purchase #5	$40.44	7.505%	$43.475	$43.48	$43.50	$43.50
Purchase #6	$200.73	11.818%	$224.4523	$224.45	$224.45	$224.50
Purchase #7	$241.82	11.854%	$270.4853	$270.49	$270.50	$270.50
7 purchase totals =	$873.24		$963.6047	$963.62	$963.65	$963.80