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	$71.57	9.737%	$78.5388	$78.54	$78.55	$78.50
Purchase #2	$106.35	13.130%	$120.3138	$120.31	$120.30	$120.30
Purchase #3	$102.80	10.749%	$113.85	$113.85	$113.85	$113.90
Purchase #4	$152.40	12.523%	$171.4851	$171.49	$171.50	$171.50
Purchase #5	$71.56	5.500%	$75.4958	$75.50	$75.50	$75.50
Purchase #6	$126.36	4.869%	$132.5125	$132.51	$132.50	$132.50
Purchase #7	$198.88	13.797%	$226.3195	$226.32	$226.30	$226.30
7 purchase totals =	$829.92		$918.5155	$918.52	$918.50	$918.50