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	$81.92	5.170%	$86.1553	$86.16	$86.15	$86.20
Purchase #2	$110.25	8.674%	$119.8131	$119.81	$119.80	$119.80
Purchase #3	$138.54	7.786%	$149.3267	$149.33	$149.35	$149.30
Purchase #4	$166.43	4.474%	$173.8761	$173.88	$173.90	$173.90
Purchase #5	$78.56	10.819%	$87.0594	$87.06	$87.05	$87.10
Purchase #6	$184.57	10.276%	$203.5364	$203.54	$203.55	$203.50
Purchase #7	$250.86	11.787%	$280.4289	$280.43	$280.45	$280.40
7 purchase totals =	$1,011.13		$1,100.1959	$1,100.21	$1,100.25	$1,100.20