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	$129.86	6.187%	$137.8944	$137.89	$137.90	$137.90
Purchase #2	$93.75	5.301%	$98.7197	$98.72	$98.70	$98.70
Purchase #3	$127.28	9.665%	$139.5816	$139.58	$139.60	$139.60
Purchase #4	$170.71	9.392%	$186.7431	$186.74	$186.75	$186.70
Purchase #5	$40.69	12.389%	$45.7311	$45.73	$45.75	$45.70
Purchase #6	$87.59	4.802%	$91.7961	$91.80	$91.80	$91.80
Purchase #7	$88.50	11.179%	$98.3934	$98.39	$98.40	$98.40
7 purchase totals =	$738.38		$798.8594	$798.85	$798.90	$798.80