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	$87.37	3.872%	$90.753	$90.75	$90.75	$90.80
Purchase #2	$170.51	10.701%	$188.7563	$188.76	$188.75	$188.80
Purchase #3	$221.54	4.502%	$231.5137	$231.51	$231.50	$231.50
Purchase #4	$61.85	8.711%	$67.2378	$67.24	$67.25	$67.20
Purchase #5	$159.70	4.494%	$166.8769	$166.88	$166.90	$166.90
Purchase #6	$104.77	3.574%	$108.5145	$108.51	$108.50	$108.50
Purchase #7	$107.31	4.874%	$112.5403	$112.54	$112.55	$112.50
7 purchase totals =	$913.05		$966.1925	$966.19	$966.20	$966.20