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	$73.49	11.720%	$82.103	$82.10	$82.10	$82.10
Purchase #2	$94.34	4.832%	$98.8985	$98.90	$98.90	$98.90
Purchase #3	$186.34	9.820%	$204.6386	$204.64	$204.65	$204.60
Purchase #4	$142.79	9.220%	$155.9552	$155.96	$155.95	$156.00
Purchase #5	$149.60	12.269%	$167.9544	$167.95	$167.95	$168.00
Purchase #6	$85.78	7.742%	$92.4211	$92.42	$92.40	$92.40
Purchase #7	$86.48	4.605%	$90.4624	$90.46	$90.45	$90.50
7 purchase totals =	$818.82		$892.4332	$892.43	$892.40	$892.50