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	$182.94	8.739%	$198.9271	$198.93	$198.95	$198.90
Purchase #2	$61.53	10.874%	$68.2208	$68.22	$68.20	$68.20
Purchase #3	$80.90	10.546%	$89.4317	$89.43	$89.45	$89.40
Purchase #4	$43.26	10.673%	$47.8771	$47.88	$47.90	$47.90
Purchase #5	$130.74	6.547%	$139.2995	$139.30	$139.30	$139.30
Purchase #6	$21.26	4.809%	$22.2824	$22.28	$22.30	$22.30
Purchase #7	$39.83	11.732%	$44.5029	$44.50	$44.50	$44.50
7 purchase totals =	$560.46		$610.5415	$610.54	$610.60	$610.50