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	$225.66	8.122%	$243.9881	$243.99	$244.00	$244.00
Purchase #2	$104.98	11.456%	$117.0065	$117.01	$117.00	$117.00
Purchase #3	$7.43	7.111%	$7.9583	$7.96	$7.95	$8.00
Purchase #4	$81.35	11.677%	$90.8492	$90.85	$90.85	$90.80
Purchase #5	$131.73	6.672%	$140.519	$140.52	$140.50	$140.50
Purchase #6	$87.52	3.138%	$90.2664	$90.27	$90.25	$90.30
Purchase #7	$142.94	9.204%	$156.0962	$156.10	$156.10	$156.10
7 purchase totals =	$781.61		$846.6837	$846.70	$846.65	$846.70