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	$140.80	3.608%	$145.8801	$145.88	$145.90	$145.90
Purchase #2	$120.47	12.320%	$135.3119	$135.31	$135.30	$135.30
Purchase #3	$161.38	6.427%	$171.7519	$171.75	$171.75	$171.80
Purchase #4	$81.95	9.223%	$89.5082	$89.51	$89.50	$89.50
Purchase #5	$230.92	5.360%	$243.2973	$243.30	$243.30	$243.30
Purchase #6	$166.85	11.337%	$185.7658	$185.77	$185.75	$185.80
Purchase #7	$16.56	12.109%	$18.5653	$18.57	$18.55	$18.60
7 purchase totals =	$918.93		$990.0805	$990.09	$990.05	$990.20