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	$143.99	6.558%	$153.4329	$153.43	$153.45	$153.40
Purchase #2	$40.73	7.784%	$43.9004	$43.90	$43.90	$43.90
Purchase #3	$203.45	4.859%	$213.3356	$213.34	$213.35	$213.30
Purchase #4	$96.96	13.663%	$110.2076	$110.21	$110.20	$110.20
Purchase #5	$148.98	13.321%	$168.8256	$168.83	$168.85	$168.80
Purchase #6	$80.51	13.404%	$91.3016	$91.30	$91.30	$91.30
Purchase #7	$201.92	8.188%	$218.4532	$218.45	$218.45	$218.50
7 purchase totals =	$916.54		$999.4569	$999.46	$999.50	$999.40