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	$122.54	13.206%	$138.7226	$138.72	$138.70	$138.70
Purchase #2	$53.99	6.590%	$57.5479	$57.55	$57.55	$57.50
Purchase #3	$67.71	7.366%	$72.6975	$72.70	$72.70	$72.70
Purchase #4	$159.30	5.664%	$168.3228	$168.32	$168.30	$168.30
Purchase #5	$156.57	10.801%	$173.4811	$173.48	$173.50	$173.50
Purchase #6	$51.65	11.425%	$57.551	$57.55	$57.55	$57.60
Purchase #7	$77.72	9.474%	$85.0832	$85.08	$85.10	$85.10
7 purchase totals =	$689.48		$753.4061	$753.40	$753.40	$753.40