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	$50.38	7.798%	$54.3086	$54.31	$54.30	$54.30
Purchase #2	$95.37	13.518%	$108.2621	$108.26	$108.25	$108.30
Purchase #3	$249.72	7.643%	$268.8061	$268.81	$268.80	$268.80
Purchase #4	$175.53	12.199%	$196.9429	$196.94	$196.95	$196.90
Purchase #5	$175.33	10.654%	$194.0097	$194.01	$194.00	$194.00
Purchase #6	$241.34	13.146%	$273.0666	$273.07	$273.05	$273.10
Purchase #7	$218.77	9.223%	$238.9472	$238.95	$238.95	$238.90
7 purchase totals =	$1,206.44		$1,334.3432	$1,334.35	$1,334.30	$1,334.30