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	$170.71	10.846%	$189.2252	$189.23	$189.25	$189.20
Purchase #2	$127.57	9.777%	$140.0425	$140.04	$140.05	$140.00
Purchase #3	$220.69	13.298%	$250.0374	$250.04	$250.05	$250.00
Purchase #4	$186.61	5.213%	$196.338	$196.34	$196.35	$196.30
Purchase #5	$58.74	10.375%	$64.8343	$64.83	$64.85	$64.80
Purchase #6	$220.55	13.662%	$250.6815	$250.68	$250.70	$250.70
Purchase #7	$250.91	12.539%	$282.3716	$282.37	$282.35	$282.40
7 purchase totals =	$1,235.78		$1,373.5305	$1,373.53	$1,373.60	$1,373.40