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	$71.86	11.687%	$80.2583	$80.26	$80.25	$80.30
Purchase #2	$82.31	10.507%	$90.9583	$90.96	$90.95	$91.00
Purchase #3	$89.32	8.668%	$97.0623	$97.06	$97.05	$97.10
Purchase #4	$82.29	8.420%	$89.2188	$89.22	$89.20	$89.20
Purchase #5	$46.37	6.566%	$49.4147	$49.41	$49.40	$49.40
Purchase #6	$111.56	7.503%	$119.9303	$119.93	$119.95	$119.90
Purchase #7	$143.79	4.334%	$150.0219	$150.02	$150.00	$150.00
7 purchase totals =	$627.50		$676.8646	$676.86	$676.80	$676.90