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	$249.47	13.335%	$282.7368	$282.74	$282.75	$282.70
Purchase #2	$218.46	11.644%	$243.8975	$243.90	$243.90	$243.90
Purchase #3	$124.69	11.589%	$139.1403	$139.14	$139.15	$139.10
Purchase #4	$89.81	8.435%	$97.3855	$97.39	$97.40	$97.40
Purchase #5	$81.37	5.117%	$85.5337	$85.53	$85.55	$85.50
Purchase #6	$193.28	6.231%	$205.3233	$205.32	$205.30	$205.30
Purchase #7	$79.74	8.431%	$86.4629	$86.46	$86.45	$86.50
7 purchase totals =	$1,036.82		$1,140.4800	$1,140.48	$1,140.50	$1,140.40