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	$138.38	5.839%	$146.46	$146.46	$146.45	$146.50
Purchase #2	$36.27	10.744%	$40.1668	$40.17	$40.15	$40.20
Purchase #3	$114.99	11.817%	$128.5784	$128.58	$128.60	$128.60
Purchase #4	$150.57	6.292%	$160.0439	$160.04	$160.05	$160.00
Purchase #5	$156.30	12.527%	$175.8797	$175.88	$175.90	$175.90
Purchase #6	$25.67	7.263%	$27.5344	$27.53	$27.55	$27.50
Purchase #7	$196.60	7.556%	$211.4551	$211.46	$211.45	$211.50
7 purchase totals =	$818.78		$890.1183	$890.12	$890.15	$890.20