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	$73.55	12.214%	$82.5334	$82.53	$82.55	$82.50
Purchase #2	$159.61	5.565%	$168.4923	$168.49	$168.50	$168.50
Purchase #3	$55.67	6.358%	$59.2095	$59.21	$59.20	$59.20
Purchase #4	$121.28	7.719%	$130.6416	$130.64	$130.65	$130.60
Purchase #5	$11.29	10.234%	$12.4454	$12.45	$12.45	$12.40
Purchase #6	$79.76	4.250%	$83.1498	$83.15	$83.15	$83.10
Purchase #7	$127.37	3.140%	$131.3694	$131.37	$131.35	$131.40
7 purchase totals =	$628.53		$667.8414	$667.84	$667.85	$667.70