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	$73.91	9.348%	$80.8191	$80.82	$80.80	$80.80
Purchase #2	$167.31	4.456%	$174.7653	$174.77	$174.75	$174.80
Purchase #3	$112.54	7.437%	$120.9096	$120.91	$120.90	$120.90
Purchase #4	$86.67	5.351%	$91.3077	$91.31	$91.30	$91.30
Purchase #5	$65.88	7.798%	$71.0173	$71.02	$71.00	$71.00
Purchase #6	$198.95	12.518%	$223.8546	$223.85	$223.85	$223.90
Purchase #7	$165.91	8.395%	$179.8381	$179.84	$179.85	$179.80
7 purchase totals =	$871.17		$942.5117	$942.52	$942.45	$942.50