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	$42.90	8.410%	$46.5079	$46.51	$46.50	$46.50
Purchase #2	$128.51	11.180%	$142.8774	$142.88	$142.90	$142.90
Purchase #3	$168.29	8.329%	$182.3069	$182.31	$182.30	$182.30
Purchase #4	$77.30	4.207%	$80.552	$80.55	$80.55	$80.60
Purchase #5	$10.98	3.192%	$11.3305	$11.33	$11.35	$11.30
Purchase #6	$48.39	10.336%	$53.3916	$53.39	$53.40	$53.40
Purchase #7	$74.60	4.559%	$78.001	$78.00	$78.00	$78.00
7 purchase totals =	$550.97		$594.9673	$594.97	$595.00	$595.00