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	$149.41	10.358%	$164.8859	$164.89	$164.90	$164.90
Purchase #2	$82.50	4.740%	$86.4105	$86.41	$86.40	$86.40
Purchase #3	$69.52	4.697%	$72.7854	$72.79	$72.80	$72.80
Purchase #4	$170.76	7.410%	$183.4133	$183.41	$183.40	$183.40
Purchase #5	$229.89	4.637%	$240.55	$240.55	$240.55	$240.60
Purchase #6	$171.30	8.637%	$186.0952	$186.10	$186.10	$186.10
Purchase #7	$41.39	7.708%	$44.5803	$44.58	$44.60	$44.60
7 purchase totals =	$914.77		$978.7206	$978.73	$978.75	$978.80