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	$79.53	11.786%	$88.9034	$88.90	$88.90	$88.90
Purchase #2	$120.73	3.344%	$124.7672	$124.77	$124.75	$124.80
Purchase #3	$148.97	7.275%	$159.8076	$159.81	$159.80	$159.80
Purchase #4	$162.30	12.680%	$182.8796	$182.88	$182.90	$182.90
Purchase #5	$140.71	7.238%	$150.8946	$150.89	$150.90	$150.90
Purchase #6	$9.80	3.570%	$10.1499	$10.15	$10.15	$10.10
Purchase #7	$158.96	4.334%	$165.8493	$165.85	$165.85	$165.80
7 purchase totals =	$821.00		$883.2516	$883.25	$883.25	$883.20