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	$34.80	5.766%	$36.8066	$36.81	$36.80	$36.80
Purchase #2	$215.32	11.719%	$240.5534	$240.55	$240.55	$240.60
Purchase #3	$82.90	13.105%	$93.764	$93.76	$93.75	$93.80
Purchase #4	$156.52	5.637%	$165.343	$165.34	$165.35	$165.30
Purchase #5	$143.34	5.257%	$150.8754	$150.88	$150.90	$150.90
Purchase #6	$155.43	12.272%	$174.5044	$174.50	$174.50	$174.50
Purchase #7	$63.72	13.194%	$72.1272	$72.13	$72.15	$72.10
7 purchase totals =	$852.03		$933.9740	$933.97	$934.00	$934.00