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	$241.28	6.115%	$256.0343	$256.03	$256.05	$256.00
Purchase #2	$59.33	13.447%	$67.3081	$67.31	$67.30	$67.30
Purchase #3	$95.57	4.454%	$99.8267	$99.83	$99.85	$99.80
Purchase #4	$243.40	5.453%	$256.6726	$256.67	$256.65	$256.70
Purchase #5	$187.80	9.820%	$206.242	$206.24	$206.25	$206.20
Purchase #6	$21.79	3.148%	$22.4759	$22.48	$22.50	$22.50
Purchase #7	$180.89	12.288%	$203.1178	$203.12	$203.10	$203.10
7 purchase totals =	$1,030.06		$1,111.6774	$1,111.68	$1,111.70	$1,111.60