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	$245.98	3.726%	$255.1452	$255.15	$255.15	$255.10
Purchase #2	$20.48	6.546%	$21.8206	$21.82	$21.80	$21.80
Purchase #3	$141.77	13.148%	$160.4099	$160.41	$160.40	$160.40
Purchase #4	$51.29	13.375%	$58.15	$58.15	$58.15	$58.20
Purchase #5	$185.56	12.559%	$208.8645	$208.86	$208.85	$208.90
Purchase #6	$77.26	10.167%	$85.115	$85.12	$85.10	$85.10
Purchase #7	$160.97	9.710%	$176.6002	$176.60	$176.60	$176.60
7 purchase totals =	$883.31		$966.1054	$966.11	$966.05	$966.10