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	$183.47	4.196%	$191.1684	$191.17	$191.15	$191.20
Purchase #2	$42.80	11.663%	$47.7918	$47.79	$47.80	$47.80
Purchase #3	$39.47	8.161%	$42.6911	$42.69	$42.70	$42.70
Purchase #4	$159.44	7.363%	$171.1796	$171.18	$171.20	$171.20
Purchase #5	$225.77	6.664%	$240.8153	$240.82	$240.80	$240.80
Purchase #6	$120.91	8.357%	$131.0144	$131.01	$131.00	$131.00
Purchase #7	$11.54	8.832%	$12.5592	$12.56	$12.55	$12.60
7 purchase totals =	$783.40		$837.2198	$837.22	$837.20	$837.30