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	$29.89	13.300%	$33.8654	$33.87	$33.85	$33.90
Purchase #2	$41.65	3.574%	$43.1386	$43.14	$43.15	$43.10
Purchase #3	$80.84	4.606%	$84.5635	$84.56	$84.55	$84.60
Purchase #4	$52.66	13.654%	$59.8502	$59.85	$59.85	$59.90
Purchase #5	$117.96	11.668%	$131.7236	$131.72	$131.70	$131.70
Purchase #6	$224.44	11.480%	$250.2057	$250.21	$250.20	$250.20
Purchase #7	$206.77	6.482%	$220.1728	$220.17	$220.15	$220.20
7 purchase totals =	$754.21		$823.5198	$823.52	$823.45	$823.60