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	$39.37	8.736%	$42.8094	$42.81	$42.80	$42.80
Purchase #2	$153.79	5.832%	$162.759	$162.76	$162.75	$162.80
Purchase #3	$162.86	5.529%	$171.8645	$171.86	$171.85	$171.90
Purchase #4	$73.59	7.284%	$78.9503	$78.95	$78.95	$79.00
Purchase #5	$76.44	9.190%	$83.4648	$83.46	$83.45	$83.50
Purchase #6	$184.45	8.519%	$200.1633	$200.16	$200.15	$200.20
Purchase #7	$187.99	5.386%	$198.1151	$198.12	$198.10	$198.10
7 purchase totals =	$878.49		$938.1264	$938.12	$938.05	$938.30