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	$178.86	3.233%	$184.6425	$184.64	$184.65	$184.60
Purchase #2	$65.37	10.279%	$72.0894	$72.09	$72.10	$72.10
Purchase #3	$90.56	9.284%	$98.9676	$98.97	$98.95	$99.00
Purchase #4	$92.96	6.681%	$99.1707	$99.17	$99.15	$99.20
Purchase #5	$29.46	9.398%	$32.2287	$32.23	$32.25	$32.20
Purchase #6	$230.48	8.841%	$250.8567	$250.86	$250.85	$250.90
Purchase #7	$108.68	3.646%	$112.6425	$112.64	$112.65	$112.60
7 purchase totals =	$796.37		$850.5981	$850.60	$850.60	$850.60