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	$70.56	8.508%	$76.5632	$76.56	$76.55	$76.60
Purchase #2	$40.33	12.216%	$45.2567	$45.26	$45.25	$45.30
Purchase #3	$106.34	5.705%	$112.4067	$112.41	$112.40	$112.40
Purchase #4	$90.97	3.149%	$93.8346	$93.83	$93.85	$93.80
Purchase #5	$189.51	12.223%	$212.6738	$212.67	$212.65	$212.70
Purchase #6	$105.69	6.685%	$112.7554	$112.76	$112.75	$112.80
Purchase #7	$36.59	3.689%	$37.9398	$37.94	$37.95	$37.90
7 purchase totals =	$639.99		$691.4302	$691.43	$691.40	$691.50