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	$115.49	11.347%	$128.5947	$128.59	$128.60	$128.60
Purchase #2	$45.91	5.155%	$48.2767	$48.28	$48.30	$48.30
Purchase #3	$102.39	3.345%	$105.8149	$105.81	$105.80	$105.80
Purchase #4	$55.35	11.818%	$61.8913	$61.89	$61.90	$61.90
Purchase #5	$192.39	12.338%	$216.1271	$216.13	$216.15	$216.10
Purchase #6	$79.35	4.676%	$83.0604	$83.06	$83.05	$83.10
Purchase #7	$171.99	6.593%	$183.3293	$183.33	$183.35	$183.30
7 purchase totals =	$762.87		$827.0944	$827.09	$827.15	$827.10