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	$78.81	5.130%	$82.853	$82.85	$82.85	$82.90
Purchase #2	$117.78	10.415%	$130.0468	$130.05	$130.05	$130.00
Purchase #3	$241.35	7.831%	$260.2501	$260.25	$260.25	$260.30
Purchase #4	$218.42	9.571%	$239.325	$239.33	$239.35	$239.30
Purchase #5	$46.57	12.309%	$52.3023	$52.30	$52.30	$52.30
Purchase #6	$199.42	11.774%	$222.8997	$222.90	$222.90	$222.90
Purchase #7	$164.25	11.566%	$183.2472	$183.25	$183.25	$183.20
7 purchase totals =	$1,066.60		$1,170.9241	$1,170.93	$1,170.95	$1,170.90