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	$158.33	12.133%	$177.5402	$177.54	$177.55	$177.50
Purchase #2	$123.91	6.240%	$131.642	$131.64	$131.65	$131.60
Purchase #3	$92.69	7.751%	$99.8744	$99.87	$99.85	$99.90
Purchase #4	$112.67	6.402%	$119.8831	$119.88	$119.90	$119.90
Purchase #5	$107.32	6.706%	$114.5169	$114.52	$114.50	$114.50
Purchase #6	$168.37	7.111%	$180.3428	$180.34	$180.35	$180.30
Purchase #7	$126.98	11.306%	$141.3364	$141.34	$141.35	$141.30
7 purchase totals =	$890.27		$965.1358	$965.13	$965.15	$965.00