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	$76.45	5.175%	$80.4063	$80.41	$80.40	$80.40
Purchase #2	$162.25	7.619%	$174.6118	$174.61	$174.60	$174.60
Purchase #3	$181.89	5.235%	$191.4119	$191.41	$191.40	$191.40
Purchase #4	$41.74	9.112%	$45.5433	$45.54	$45.55	$45.50
Purchase #5	$34.32	12.601%	$38.6447	$38.64	$38.65	$38.60
Purchase #6	$219.87	10.355%	$242.6375	$242.64	$242.65	$242.60
Purchase #7	$139.67	7.525%	$150.1802	$150.18	$150.20	$150.20
7 purchase totals =	$856.19		$923.4357	$923.43	$923.45	$923.30