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	$249.51	8.366%	$270.384	$270.38	$270.40	$270.40
Purchase #2	$198.48	11.860%	$222.0197	$222.02	$222.00	$222.00
Purchase #3	$157.51	9.713%	$172.8089	$172.81	$172.80	$172.80
Purchase #4	$44.83	13.160%	$50.7296	$50.73	$50.75	$50.70
Purchase #5	$56.28	11.798%	$62.9199	$62.92	$62.90	$62.90
Purchase #6	$112.63	12.165%	$126.3314	$126.33	$126.35	$126.30
Purchase #7	$147.55	8.614%	$160.26	$160.26	$160.25	$160.30
7 purchase totals =	$966.79		$1,065.4535	$1,065.45	$1,065.45	$1,065.40