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	$184.25	6.854%	$196.8785	$196.88	$196.90	$196.90
Purchase #2	$134.51	8.785%	$146.3267	$146.33	$146.35	$146.30
Purchase #3	$31.53	4.792%	$33.0409	$33.04	$33.05	$33.00
Purchase #4	$178.56	8.735%	$194.1572	$194.16	$194.15	$194.20
Purchase #5	$56.95	8.121%	$61.5749	$61.57	$61.55	$61.60
Purchase #6	$107.83	13.156%	$122.0161	$122.02	$122.00	$122.00
Purchase #7	$106.86	9.650%	$117.172	$117.17	$117.15	$117.20
7 purchase totals =	$800.49		$871.1663	$871.17	$871.15	$871.20