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	$73.40	11.834%	$82.0862	$82.09	$82.10	$82.10
Purchase #2	$195.51	13.443%	$221.7924	$221.79	$221.80	$221.80
Purchase #3	$182.58	9.196%	$199.3701	$199.37	$199.35	$199.40
Purchase #4	$77.83	6.486%	$82.8781	$82.88	$82.90	$82.90
Purchase #5	$133.30	10.425%	$147.1965	$147.20	$147.20	$147.20
Purchase #6	$43.74	5.471%	$46.133	$46.13	$46.15	$46.10
Purchase #7	$245.28	6.132%	$260.3206	$260.32	$260.30	$260.30
7 purchase totals =	$951.64		$1,039.7769	$1,039.78	$1,039.80	$1,039.80