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	$94.41	5.302%	$99.4156	$99.42	$99.40	$99.40
Purchase #2	$100.86	10.474%	$111.4241	$111.42	$111.40	$111.40
Purchase #3	$157.41	9.165%	$171.8366	$171.84	$171.85	$171.80
Purchase #4	$215.47	13.297%	$244.121	$244.12	$244.10	$244.10
Purchase #5	$76.44	11.274%	$85.0578	$85.06	$85.05	$85.10
Purchase #6	$105.40	5.320%	$111.0073	$111.01	$111.00	$111.00
Purchase #7	$90.57	10.296%	$99.8951	$99.90	$99.90	$99.90
7 purchase totals =	$840.56		$922.7575	$922.77	$922.70	$922.70