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	$38.90	8.821%	$42.3314	$42.33	$42.35	$42.30
Purchase #2	$157.68	3.571%	$163.3108	$163.31	$163.30	$163.30
Purchase #3	$198.32	5.405%	$209.0392	$209.04	$209.05	$209.00
Purchase #4	$170.69	8.184%	$184.6593	$184.66	$184.65	$184.70
Purchase #5	$95.79	10.150%	$105.5127	$105.51	$105.50	$105.50
Purchase #6	$68.89	4.697%	$72.1258	$72.13	$72.15	$72.10
Purchase #7	$6.89	8.144%	$7.4511	$7.45	$7.45	$7.50
7 purchase totals =	$737.16		$784.4303	$784.43	$784.45	$784.40