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	$201.38	9.659%	$220.8313	$220.83	$220.85	$220.80
Purchase #2	$248.36	10.554%	$274.5719	$274.57	$274.55	$274.60
Purchase #3	$91.75	8.111%	$99.1918	$99.19	$99.20	$99.20
Purchase #4	$193.76	12.589%	$218.1524	$218.15	$218.15	$218.20
Purchase #5	$102.90	12.740%	$116.0095	$116.01	$116.00	$116.00
Purchase #6	$126.95	3.636%	$131.5659	$131.57	$131.55	$131.60
Purchase #7	$90.73	10.253%	$100.0325	$100.03	$100.05	$100.00
7 purchase totals =	$1,055.83		$1,160.3553	$1,160.35	$1,160.35	$1,160.40