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	$23.74	7.650%	$25.5561	$25.56	$25.55	$25.60
Purchase #2	$106.89	10.440%	$118.0493	$118.05	$118.05	$118.00
Purchase #3	$94.83	11.432%	$105.671	$105.67	$105.65	$105.70
Purchase #4	$95.66	9.315%	$104.5707	$104.57	$104.55	$104.60
Purchase #5	$91.46	4.538%	$95.6105	$95.61	$95.60	$95.60
Purchase #6	$88.37	13.119%	$99.9633	$99.96	$99.95	$100.00
Purchase #7	$249.50	11.345%	$277.8058	$277.81	$277.80	$277.80
7 purchase totals =	$750.45		$827.2267	$827.23	$827.15	$827.30