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	$149.91	4.216%	$156.2302	$156.23	$156.25	$156.20
Purchase #2	$146.63	10.145%	$161.5056	$161.51	$161.50	$161.50
Purchase #3	$185.53	5.614%	$195.9457	$195.95	$195.95	$195.90
Purchase #4	$71.43	10.510%	$78.9373	$78.94	$78.95	$78.90
Purchase #5	$127.78	9.524%	$139.9498	$139.95	$139.95	$139.90
Purchase #6	$131.54	4.673%	$137.6869	$137.69	$137.70	$137.70
Purchase #7	$55.59	12.709%	$62.6549	$62.65	$62.65	$62.70
7 purchase totals =	$868.41		$932.9104	$932.92	$932.95	$932.80