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	$81.34	10.505%	$89.8848	$89.88	$89.90	$89.90
Purchase #2	$26.78	12.421%	$30.1063	$30.11	$30.10	$30.10
Purchase #3	$7.37	4.306%	$7.6874	$7.69	$7.70	$7.70
Purchase #4	$164.54	3.288%	$169.9501	$169.95	$169.95	$170.00
Purchase #5	$164.61	8.165%	$178.0504	$178.05	$178.05	$178.10
Purchase #6	$208.60	8.109%	$225.5154	$225.52	$225.50	$225.50
Purchase #7	$131.48	8.679%	$142.8911	$142.89	$142.90	$142.90
7 purchase totals =	$784.72		$844.0855	$844.09	$844.10	$844.20