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	$31.37	4.841%	$32.8886	$32.89	$32.90	$32.90
Purchase #2	$134.34	6.758%	$143.4187	$143.42	$143.40	$143.40
Purchase #3	$114.59	4.550%	$119.8038	$119.80	$119.80	$119.80
Purchase #4	$91.98	4.360%	$95.9903	$95.99	$96.00	$96.00
Purchase #5	$120.56	6.278%	$128.1288	$128.13	$128.15	$128.10
Purchase #6	$112.75	9.747%	$123.7397	$123.74	$123.75	$123.70
Purchase #7	$133.92	4.714%	$140.233	$140.23	$140.25	$140.20
7 purchase totals =	$739.51		$784.2029	$784.20	$784.25	$784.10