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	$32.55	7.199%	$34.8933	$34.89	$34.90	$34.90
Purchase #2	$46.50	5.383%	$49.0031	$49.00	$49.00	$49.00
Purchase #3	$78.71	9.220%	$85.9671	$85.97	$85.95	$86.00
Purchase #4	$34.59	9.774%	$37.9708	$37.97	$37.95	$38.00
Purchase #5	$80.65	10.700%	$89.2796	$89.28	$89.30	$89.30
Purchase #6	$233.46	12.368%	$262.3343	$262.33	$262.35	$262.30
Purchase #7	$165.38	8.231%	$178.9924	$178.99	$179.00	$179.00
7 purchase totals =	$671.84		$738.4406	$738.43	$738.45	$738.50