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	$124.33	12.517%	$139.8924	$139.89	$139.90	$139.90
Purchase #2	$235.39	7.496%	$253.0348	$253.03	$253.05	$253.00
Purchase #3	$34.28	12.301%	$38.4968	$38.50	$38.50	$38.50
Purchase #4	$56.89	4.488%	$59.4432	$59.44	$59.45	$59.40
Purchase #5	$191.97	3.549%	$198.783	$198.78	$198.80	$198.80
Purchase #6	$208.42	11.274%	$231.9173	$231.92	$231.90	$231.90
Purchase #7	$80.37	10.102%	$88.489	$88.49	$88.50	$88.50
7 purchase totals =	$931.65		$1,010.0565	$1,010.05	$1,010.10	$1,010.00