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	$80.25	9.788%	$88.1049	$88.10	$88.10	$88.10
Purchase #2	$182.45	9.696%	$200.1404	$200.14	$200.15	$200.10
Purchase #3	$39.56	5.740%	$41.8307	$41.83	$41.85	$41.80
Purchase #4	$86.60	9.722%	$95.0193	$95.02	$95.00	$95.00
Purchase #5	$208.41	9.619%	$228.457	$228.46	$228.45	$228.50
Purchase #6	$92.78	6.814%	$99.102	$99.10	$99.10	$99.10
Purchase #7	$126.45	3.180%	$130.4711	$130.47	$130.45	$130.50
7 purchase totals =	$816.50		$883.1254	$883.12	$883.10	$883.10