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	$67.82	8.836%	$73.8126	$73.81	$73.80	$73.80
Purchase #2	$104.86	13.862%	$119.3957	$119.40	$119.40	$119.40
Purchase #3	$247.34	10.507%	$273.328	$273.33	$273.35	$273.30
Purchase #4	$250.62	5.291%	$263.8803	$263.88	$263.90	$263.90
Purchase #5	$79.85	12.414%	$89.7626	$89.76	$89.75	$89.80
Purchase #6	$219.86	5.469%	$231.8841	$231.88	$231.90	$231.90
Purchase #7	$229.98	10.626%	$254.4177	$254.42	$254.40	$254.40
7 purchase totals =	$1,200.33		$1,306.4810	$1,306.48	$1,306.50	$1,306.50