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	$98.91	5.443%	$104.2937	$104.29	$104.30	$104.30
Purchase #2	$203.90	11.143%	$226.6206	$226.62	$226.60	$226.60
Purchase #3	$67.90	3.800%	$70.4802	$70.48	$70.50	$70.50
Purchase #4	$156.87	7.301%	$168.3231	$168.32	$168.30	$168.30
Purchase #5	$103.82	8.397%	$112.5378	$112.54	$112.55	$112.50
Purchase #6	$80.86	10.178%	$89.0899	$89.09	$89.10	$89.10
Purchase #7	$178.93	12.370%	$201.0636	$201.06	$201.05	$201.10
7 purchase totals =	$891.19		$972.4089	$972.40	$972.40	$972.40