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	$67.67	8.301%	$73.2873	$73.29	$73.30	$73.30
Purchase #2	$124.66	11.132%	$138.5372	$138.54	$138.55	$138.50
Purchase #3	$44.54	3.385%	$46.0477	$46.05	$46.05	$46.00
Purchase #4	$229.72	7.365%	$246.6389	$246.64	$246.65	$246.60
Purchase #5	$38.69	8.604%	$42.0189	$42.02	$42.00	$42.00
Purchase #6	$68.90	5.679%	$72.8128	$72.81	$72.80	$72.80
Purchase #7	$35.60	13.694%	$40.4751	$40.48	$40.50	$40.50
7 purchase totals =	$609.78		$659.8179	$659.83	$659.85	$659.70