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	$49.60	7.785%	$53.4614	$53.46	$53.45	$53.50
Purchase #2	$45.38	13.533%	$51.5213	$51.52	$51.50	$51.50
Purchase #3	$201.44	6.836%	$215.2104	$215.21	$215.20	$215.20
Purchase #4	$63.47	13.264%	$71.8887	$71.89	$71.90	$71.90
Purchase #5	$10.90	7.626%	$11.7312	$11.73	$11.75	$11.70
Purchase #6	$195.72	10.614%	$216.4937	$216.49	$216.50	$216.50
Purchase #7	$185.82	7.356%	$199.4889	$199.49	$199.50	$199.50
7 purchase totals =	$752.33		$819.7956	$819.79	$819.80	$819.80