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	$154.48	6.238%	$164.1165	$164.12	$164.10	$164.10
Purchase #2	$78.41	12.776%	$88.4277	$88.43	$88.45	$88.40
Purchase #3	$114.75	11.345%	$127.7684	$127.77	$127.75	$127.80
Purchase #4	$206.63	12.474%	$232.405	$232.41	$232.40	$232.40
Purchase #5	$136.40	4.187%	$142.1111	$142.11	$142.10	$142.10
Purchase #6	$185.72	5.626%	$196.1686	$196.17	$196.15	$196.20
Purchase #7	$160.72	9.128%	$175.3905	$175.39	$175.40	$175.40
7 purchase totals =	$1,037.11		$1,126.3878	$1,126.40	$1,126.35	$1,126.40