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	$106.79	13.335%	$121.0304	$121.03	$121.05	$121.00
Purchase #2	$51.59	7.521%	$55.4701	$55.47	$55.45	$55.50
Purchase #3	$174.98	12.520%	$196.8875	$196.89	$196.90	$196.90
Purchase #4	$84.46	6.840%	$90.2371	$90.24	$90.25	$90.20
Purchase #5	$49.87	11.117%	$55.414	$55.41	$55.40	$55.40
Purchase #6	$186.25	13.742%	$211.8445	$211.84	$211.85	$211.80
Purchase #7	$57.38	3.821%	$59.5725	$59.57	$59.55	$59.60
7 purchase totals =	$711.32		$790.4561	$790.45	$790.45	$790.40