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	$130.45	4.646%	$136.5107	$136.51	$136.50	$136.50
Purchase #2	$161.36	4.846%	$169.1795	$169.18	$169.20	$169.20
Purchase #3	$66.34	9.460%	$72.6158	$72.62	$72.60	$72.60
Purchase #4	$41.75	5.147%	$43.8989	$43.90	$43.90	$43.90
Purchase #5	$223.84	8.702%	$243.3186	$243.32	$243.30	$243.30
Purchase #6	$77.34	4.540%	$80.8512	$80.85	$80.85	$80.90
Purchase #7	$231.61	13.697%	$263.3336	$263.33	$263.35	$263.30
7 purchase totals =	$932.69		$1,009.7083	$1,009.71	$1,009.70	$1,009.70