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	$17.39	4.735%	$18.2134	$18.21	$18.20	$18.20
Purchase #2	$39.63	7.672%	$42.6704	$42.67	$42.65	$42.70
Purchase #3	$186.53	5.390%	$196.584	$196.58	$196.60	$196.60
Purchase #4	$56.98	13.503%	$64.674	$64.67	$64.65	$64.70
Purchase #5	$195.76	8.216%	$211.8436	$211.84	$211.85	$211.80
Purchase #6	$144.25	3.560%	$149.3853	$149.39	$149.40	$149.40
Purchase #7	$131.71	3.661%	$136.5319	$136.53	$136.55	$136.50
7 purchase totals =	$772.25		$819.9026	$819.89	$819.90	$819.90