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	$78.91	9.301%	$86.2494	$86.25	$86.25	$86.20
Purchase #2	$79.58	12.507%	$89.5331	$89.53	$89.55	$89.50
Purchase #3	$12.36	13.801%	$14.0658	$14.07	$14.05	$14.10
Purchase #4	$139.41	11.574%	$155.5453	$155.55	$155.55	$155.50
Purchase #5	$45.99	3.351%	$47.5311	$47.53	$47.55	$47.50
Purchase #6	$6.94	7.711%	$7.4751	$7.48	$7.50	$7.50
Purchase #7	$168.26	12.784%	$189.7704	$189.77	$189.75	$189.80
7 purchase totals =	$531.45		$590.1702	$590.18	$590.20	$590.10