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	$42.32	8.265%	$45.8177	$45.82	$45.80	$45.80
Purchase #2	$118.71	4.495%	$124.046	$124.05	$124.05	$124.00
Purchase #3	$229.89	3.760%	$238.5339	$238.53	$238.55	$238.50
Purchase #4	$62.83	7.120%	$67.3035	$67.30	$67.30	$67.30
Purchase #5	$144.82	11.184%	$161.0167	$161.02	$161.00	$161.00
Purchase #6	$126.43	4.188%	$131.7249	$131.72	$131.70	$131.70
Purchase #7	$155.40	8.540%	$168.6712	$168.67	$168.65	$168.70
7 purchase totals =	$880.40		$937.1139	$937.11	$937.05	$937.00