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	$209.27	7.289%	$224.5237	$224.52	$224.50	$224.50
Purchase #2	$136.98	3.275%	$141.4661	$141.47	$141.45	$141.50
Purchase #3	$143.52	13.743%	$163.244	$163.24	$163.25	$163.20
Purchase #4	$152.46	11.426%	$169.8801	$169.88	$169.90	$169.90
Purchase #5	$72.61	12.191%	$81.4619	$81.46	$81.45	$81.50
Purchase #6	$6.46	13.299%	$7.3191	$7.32	$7.30	$7.30
Purchase #7	$16.46	11.183%	$18.3007	$18.30	$18.30	$18.30
7 purchase totals =	$737.76		$806.1956	$806.19	$806.15	$806.20