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	$88.32	13.751%	$100.4649	$100.46	$100.45	$100.50
Purchase #2	$37.47	6.168%	$39.7811	$39.78	$39.80	$39.80
Purchase #3	$213.88	10.506%	$236.3502	$236.35	$236.35	$236.40
Purchase #4	$67.54	5.509%	$71.2608	$71.26	$71.25	$71.30
Purchase #5	$169.49	11.832%	$189.5441	$189.54	$189.55	$189.50
Purchase #6	$176.34	9.750%	$193.5332	$193.53	$193.55	$193.50
Purchase #7	$236.76	11.318%	$263.5565	$263.56	$263.55	$263.60
7 purchase totals =	$989.80		$1,094.4908	$1,094.48	$1,094.50	$1,094.60