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	$38.31	11.335%	$42.6524	$42.65	$42.65	$42.70
Purchase #2	$60.34	11.104%	$67.0402	$67.04	$67.05	$67.00
Purchase #3	$220.92	13.238%	$250.1654	$250.17	$250.15	$250.20
Purchase #4	$197.82	9.305%	$216.2272	$216.23	$216.25	$216.20
Purchase #5	$79.46	11.475%	$88.578	$88.58	$88.60	$88.60
Purchase #6	$168.52	12.318%	$189.2783	$189.28	$189.30	$189.30
Purchase #7	$224.59	3.302%	$232.006	$232.01	$232.00	$232.00
7 purchase totals =	$989.96		$1,085.9475	$1,085.96	$1,086.00	$1,086.00