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	$38.54	11.254%	$42.8773	$42.88	$42.90	$42.90
Purchase #2	$112.83	8.173%	$122.0516	$122.05	$122.05	$122.10
Purchase #3	$143.30	10.824%	$158.8108	$158.81	$158.80	$158.80
Purchase #4	$185.33	5.812%	$196.1014	$196.10	$196.10	$196.10
Purchase #5	$91.55	12.716%	$103.1915	$103.19	$103.20	$103.20
Purchase #6	$198.48	10.282%	$218.8877	$218.89	$218.90	$218.90
Purchase #7	$197.89	12.819%	$223.2575	$223.26	$223.25	$223.30
7 purchase totals =	$967.92		$1,065.1778	$1,065.18	$1,065.20	$1,065.30