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	$73.86	11.462%	$82.3258	$82.33	$82.35	$82.30
Purchase #2	$119.99	13.674%	$136.3974	$136.40	$136.40	$136.40
Purchase #3	$23.43	8.246%	$25.362	$25.36	$25.35	$25.40
Purchase #4	$80.77	12.133%	$90.5698	$90.57	$90.55	$90.60
Purchase #5	$178.26	10.218%	$196.4746	$196.47	$196.45	$196.50
Purchase #6	$89.67	8.437%	$97.2355	$97.24	$97.25	$97.20
Purchase #7	$159.70	9.519%	$174.9018	$174.90	$174.90	$174.90
7 purchase totals =	$725.68		$803.2669	$803.27	$803.25	$803.30