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	$130.39	6.302%	$138.6072	$138.61	$138.60	$138.60
Purchase #2	$52.91	11.314%	$58.8962	$58.90	$58.90	$58.90
Purchase #3	$147.33	3.526%	$152.5249	$152.52	$152.50	$152.50
Purchase #4	$240.76	12.405%	$270.6263	$270.63	$270.65	$270.60
Purchase #5	$152.83	8.590%	$165.9581	$165.96	$165.95	$166.00
Purchase #6	$53.72	7.445%	$57.7195	$57.72	$57.70	$57.70
Purchase #7	$40.83	12.792%	$46.053	$46.05	$46.05	$46.10
7 purchase totals =	$818.77		$890.3852	$890.39	$890.35	$890.40