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	$137.93	13.253%	$156.2099	$156.21	$156.20	$156.20
Purchase #2	$69.99	3.830%	$72.6706	$72.67	$72.65	$72.70
Purchase #3	$30.51	10.270%	$33.6434	$33.64	$33.65	$33.60
Purchase #4	$91.25	13.647%	$103.7029	$103.70	$103.70	$103.70
Purchase #5	$120.35	7.712%	$129.6314	$129.63	$129.65	$129.60
Purchase #6	$35.25	12.197%	$39.5494	$39.55	$39.55	$39.50
Purchase #7	$123.26	6.681%	$131.495	$131.50	$131.50	$131.50
7 purchase totals =	$608.54		$666.9026	$666.90	$666.90	$666.80