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	$93.26	3.458%	$96.4849	$96.48	$96.50	$96.50
Purchase #2	$80.50	3.693%	$83.4729	$83.47	$83.45	$83.50
Purchase #3	$92.61	7.868%	$99.8966	$99.90	$99.90	$99.90
Purchase #4	$198.75	12.149%	$222.8961	$222.90	$222.90	$222.90
Purchase #5	$87.61	5.390%	$92.3322	$92.33	$92.35	$92.30
Purchase #6	$189.31	5.672%	$200.0477	$200.05	$200.05	$200.00
Purchase #7	$73.31	13.554%	$83.2464	$83.25	$83.25	$83.20
7 purchase totals =	$815.35		$878.3768	$878.38	$878.40	$878.30