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	$48.32	8.623%	$52.4866	$52.49	$52.50	$52.50
Purchase #2	$248.47	13.244%	$281.3774	$281.38	$281.40	$281.40
Purchase #3	$239.82	12.785%	$270.481	$270.48	$270.50	$270.50
Purchase #4	$149.33	10.278%	$164.6781	$164.68	$164.70	$164.70
Purchase #5	$242.85	6.742%	$259.2229	$259.22	$259.20	$259.20
Purchase #6	$88.29	13.337%	$100.0652	$100.07	$100.05	$100.10
Purchase #7	$174.28	6.233%	$185.1429	$185.14	$185.15	$185.10
7 purchase totals =	$1,191.36		$1,313.4541	$1,313.46	$1,313.50	$1,313.50