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	$79.60	4.316%	$83.0355	$83.04	$83.05	$83.00
Purchase #2	$53.93	5.339%	$56.8093	$56.81	$56.80	$56.80
Purchase #3	$122.98	7.696%	$132.4445	$132.44	$132.45	$132.40
Purchase #4	$110.51	11.466%	$123.1811	$123.18	$123.20	$123.20
Purchase #5	$248.73	8.578%	$270.0661	$270.07	$270.05	$270.10
Purchase #6	$201.56	10.381%	$222.4839	$222.48	$222.50	$222.50
Purchase #7	$203.46	4.457%	$212.5282	$212.53	$212.55	$212.50
7 purchase totals =	$1,020.77		$1,100.5486	$1,100.55	$1,100.60	$1,100.50