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	$82.30	8.693%	$89.4543	$89.45	$89.45	$89.50
Purchase #2	$155.77	10.372%	$171.9265	$171.93	$171.95	$171.90
Purchase #3	$95.91	9.790%	$105.2996	$105.30	$105.30	$105.30
Purchase #4	$222.90	8.588%	$242.0427	$242.04	$242.05	$242.00
Purchase #5	$188.89	8.688%	$205.3008	$205.30	$205.30	$205.30
Purchase #6	$47.35	4.411%	$49.4386	$49.44	$49.45	$49.40
Purchase #7	$71.44	10.421%	$78.8848	$78.88	$78.90	$78.90
7 purchase totals =	$864.56		$942.3473	$942.34	$942.40	$942.30