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	$93.35	7.724%	$100.5604	$100.56	$100.55	$100.60
Purchase #2	$89.35	3.794%	$92.7399	$92.74	$92.75	$92.70
Purchase #3	$78.47	6.665%	$83.7	$83.70	$83.70	$83.70
Purchase #4	$28.34	10.744%	$31.3848	$31.38	$31.40	$31.40
Purchase #5	$78.51	10.159%	$86.4858	$86.49	$86.50	$86.50
Purchase #6	$75.36	3.218%	$77.7851	$77.79	$77.80	$77.80
Purchase #7	$80.59	12.645%	$90.7806	$90.78	$90.80	$90.80
7 purchase totals =	$523.97		$563.4366	$563.44	$563.50	$563.50