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	$103.92	9.574%	$113.8693	$113.87	$113.85	$113.90
Purchase #2	$13.39	12.813%	$15.1057	$15.11	$15.10	$15.10
Purchase #3	$170.26	5.470%	$179.5732	$179.57	$179.55	$179.60
Purchase #4	$244.83	11.771%	$273.6489	$273.65	$273.65	$273.60
Purchase #5	$98.31	12.477%	$110.5761	$110.58	$110.60	$110.60
Purchase #6	$186.50	5.571%	$196.8899	$196.89	$196.90	$196.90
Purchase #7	$32.68	3.709%	$33.8921	$33.89	$33.90	$33.90
7 purchase totals =	$849.89		$923.5552	$923.56	$923.55	$923.60