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	$152.83	7.646%	$164.5154	$164.52	$164.50	$164.50
Purchase #2	$147.51	10.446%	$162.9189	$162.92	$162.90	$162.90
Purchase #3	$206.88	7.855%	$223.1304	$223.13	$223.15	$223.10
Purchase #4	$145.91	9.426%	$159.6635	$159.66	$159.65	$159.70
Purchase #5	$158.37	8.383%	$171.6462	$171.65	$171.65	$171.60
Purchase #6	$175.29	8.200%	$189.6638	$189.66	$189.65	$189.70
Purchase #7	$196.86	12.725%	$221.9104	$221.91	$221.90	$221.90
7 purchase totals =	$1,183.65		$1,293.4486	$1,293.45	$1,293.40	$1,293.40