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	$81.30	11.295%	$90.4828	$90.48	$90.50	$90.50
Purchase #2	$170.46	10.336%	$188.0787	$188.08	$188.10	$188.10
Purchase #3	$86.47	5.486%	$91.2137	$91.21	$91.20	$91.20
Purchase #4	$13.51	7.774%	$14.5603	$14.56	$14.55	$14.60
Purchase #5	$62.84	13.641%	$71.412	$71.41	$71.40	$71.40
Purchase #6	$226.31	11.858%	$253.1458	$253.15	$253.15	$253.10
Purchase #7	$158.91	3.237%	$164.0539	$164.05	$164.05	$164.10
7 purchase totals =	$799.80		$872.9472	$872.94	$872.95	$873.00