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	$75.33	3.759%	$78.1617	$78.16	$78.15	$78.20
Purchase #2	$245.54	10.698%	$271.8079	$271.81	$271.80	$271.80
Purchase #3	$78.91	9.795%	$86.6392	$86.64	$86.65	$86.60
Purchase #4	$82.77	4.363%	$86.3813	$86.38	$86.40	$86.40
Purchase #5	$30.71	8.830%	$33.4217	$33.42	$33.40	$33.40
Purchase #6	$108.49	3.459%	$112.2427	$112.24	$112.25	$112.20
Purchase #7	$113.84	8.262%	$123.2455	$123.25	$123.25	$123.20
7 purchase totals =	$735.59		$791.9000	$791.90	$791.90	$791.80