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	$193.86	12.865%	$218.8001	$218.80	$218.80	$218.80
Purchase #2	$156.52	12.446%	$176.0005	$176.00	$176.00	$176.00
Purchase #3	$72.77	4.260%	$75.87	$75.87	$75.85	$75.90
Purchase #4	$247.51	3.248%	$255.5491	$255.55	$255.55	$255.50
Purchase #5	$73.59	5.148%	$77.3784	$77.38	$77.40	$77.40
Purchase #6	$62.83	5.808%	$66.4792	$66.48	$66.50	$66.50
Purchase #7	$245.46	12.124%	$275.2196	$275.22	$275.20	$275.20
7 purchase totals =	$1,052.54		$1,145.2969	$1,145.30	$1,145.30	$1,145.30