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	$52.34	3.384%	$54.1112	$54.11	$54.10	$54.10
Purchase #2	$52.41	9.741%	$57.5153	$57.52	$57.50	$57.50
Purchase #3	$38.72	12.432%	$43.5337	$43.53	$43.55	$43.50
Purchase #4	$155.25	12.389%	$174.4839	$174.48	$174.50	$174.50
Purchase #5	$135.94	3.366%	$140.5157	$140.52	$140.50	$140.50
Purchase #6	$136.69	6.432%	$145.4819	$145.48	$145.50	$145.50
Purchase #7	$113.30	12.519%	$127.484	$127.48	$127.50	$127.50
7 purchase totals =	$684.65		$743.1257	$743.12	$743.15	$743.10