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	$93.44	6.700%	$99.7005	$99.70	$99.70	$99.70
Purchase #2	$123.38	12.680%	$139.0246	$139.02	$139.00	$139.00
Purchase #3	$122.48	4.459%	$127.9414	$127.94	$127.95	$127.90
Purchase #4	$112.81	13.459%	$127.9931	$127.99	$128.00	$128.00
Purchase #5	$39.59	7.387%	$42.5145	$42.51	$42.50	$42.50
Purchase #6	$249.60	7.437%	$268.1628	$268.16	$268.15	$268.20
Purchase #7	$191.28	10.301%	$210.9838	$210.98	$211.00	$211.00
7 purchase totals =	$932.58		$1,016.3207	$1,016.30	$1,016.30	$1,016.30