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	$39.91	9.757%	$43.804	$43.80	$43.80	$43.80
Purchase #2	$155.67	3.346%	$160.8787	$160.88	$160.90	$160.90
Purchase #3	$158.99	6.614%	$169.5056	$169.51	$169.50	$169.50
Purchase #4	$126.38	4.760%	$132.3957	$132.40	$132.40	$132.40
Purchase #5	$105.88	3.818%	$109.9225	$109.92	$109.90	$109.90
Purchase #6	$165.40	8.321%	$179.1629	$179.16	$179.15	$179.20
Purchase #7	$233.33	7.371%	$250.5288	$250.53	$250.55	$250.50
7 purchase totals =	$985.56		$1,046.1982	$1,046.20	$1,046.20	$1,046.20