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	$15.55	7.462%	$16.7103	$16.71	$16.70	$16.70
Purchase #2	$28.92	13.193%	$32.7354	$32.74	$32.75	$32.70
Purchase #3	$47.27	3.124%	$48.7467	$48.75	$48.75	$48.70
Purchase #4	$196.59	13.680%	$223.4835	$223.48	$223.50	$223.50
Purchase #5	$229.29	11.670%	$256.0481	$256.05	$256.05	$256.00
Purchase #6	$77.89	9.830%	$85.5466	$85.55	$85.55	$85.50
Purchase #7	$219.73	11.651%	$245.3307	$245.33	$245.35	$245.30
7 purchase totals =	$815.24		$908.6013	$908.61	$908.65	$908.40