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	$130.89	6.873%	$139.8861	$139.89	$139.90	$139.90
Purchase #2	$94.84	3.810%	$98.4534	$98.45	$98.45	$98.50
Purchase #3	$148.76	5.760%	$157.3286	$157.33	$157.35	$157.30
Purchase #4	$35.69	10.727%	$39.5185	$39.52	$39.50	$39.50
Purchase #5	$88.33	3.483%	$91.4065	$91.41	$91.40	$91.40
Purchase #6	$217.26	9.115%	$237.0632	$237.06	$237.05	$237.10
Purchase #7	$145.95	13.334%	$165.411	$165.41	$165.40	$165.40
7 purchase totals =	$861.72		$929.0673	$929.07	$929.05	$929.10