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	$92.33	7.369%	$99.1338	$99.13	$99.15	$99.10
Purchase #2	$67.77	13.350%	$76.8173	$76.82	$76.80	$76.80
Purchase #3	$71.39	9.596%	$78.2406	$78.24	$78.25	$78.20
Purchase #4	$123.59	4.664%	$129.3542	$129.35	$129.35	$129.40
Purchase #5	$62.81	4.836%	$65.8475	$65.85	$65.85	$65.80
Purchase #6	$248.49	9.273%	$271.5325	$271.53	$271.55	$271.50
Purchase #7	$214.79	13.566%	$243.9284	$243.93	$243.95	$243.90
7 purchase totals =	$881.17		$964.8543	$964.85	$964.90	$964.70