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	$129.59	7.654%	$139.5088	$139.51	$139.50	$139.50
Purchase #2	$156.79	5.682%	$165.6988	$165.70	$165.70	$165.70
Purchase #3	$207.71	7.289%	$222.85	$222.85	$222.85	$222.90
Purchase #4	$66.69	5.538%	$70.3833	$70.38	$70.40	$70.40
Purchase #5	$82.96	13.627%	$94.265	$94.27	$94.25	$94.30
Purchase #6	$199.53	13.722%	$226.9095	$226.91	$226.90	$226.90
Purchase #7	$12.26	7.393%	$13.1664	$13.17	$13.15	$13.20
7 purchase totals =	$855.53		$932.7818	$932.79	$932.75	$932.90