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	$70.53	13.811%	$80.2709	$80.27	$80.25	$80.30
Purchase #2	$28.46	11.221%	$31.6535	$31.65	$31.65	$31.70
Purchase #3	$55.82	13.126%	$63.1469	$63.15	$63.15	$63.10
Purchase #4	$62.56	11.122%	$69.5179	$69.52	$69.50	$69.50
Purchase #5	$85.88	3.267%	$88.6857	$88.69	$88.70	$88.70
Purchase #6	$82.97	6.641%	$88.48	$88.48	$88.50	$88.50
Purchase #7	$222.82	8.637%	$242.065	$242.07	$242.05	$242.10
7 purchase totals =	$609.04		$663.8199	$663.83	$663.80	$663.90