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	$234.51	11.128%	$260.6063	$260.61	$260.60	$260.60
Purchase #2	$195.89	6.570%	$208.76	$208.76	$208.75	$208.80
Purchase #3	$76.71	9.348%	$83.8809	$83.88	$83.90	$83.90
Purchase #4	$134.45	13.518%	$152.625	$152.63	$152.65	$152.60
Purchase #5	$89.35	12.814%	$100.7993	$100.80	$100.80	$100.80
Purchase #6	$123.55	6.492%	$131.5709	$131.57	$131.55	$131.60
Purchase #7	$70.65	12.736%	$79.648	$79.65	$79.65	$79.60
7 purchase totals =	$925.11		$1,017.8904	$1,017.90	$1,017.90	$1,017.90