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	$56.28	6.401%	$59.8825	$59.88	$59.90	$59.90
Purchase #2	$52.31	6.421%	$55.6688	$55.67	$55.65	$55.70
Purchase #3	$78.28	3.703%	$81.1787	$81.18	$81.20	$81.20
Purchase #4	$104.69	10.843%	$116.0415	$116.04	$116.05	$116.00
Purchase #5	$210.90	5.285%	$222.0461	$222.05	$222.05	$222.00
Purchase #6	$136.79	9.568%	$149.8781	$149.88	$149.90	$149.90
Purchase #7	$118.86	7.629%	$127.9278	$127.93	$127.95	$127.90
7 purchase totals =	$758.11		$812.6235	$812.63	$812.70	$812.60