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	$112.74	13.102%	$127.5112	$127.51	$127.50	$127.50
Purchase #2	$214.89	8.650%	$233.478	$233.48	$233.50	$233.50
Purchase #3	$55.92	4.429%	$58.3967	$58.40	$58.40	$58.40
Purchase #4	$68.27	7.245%	$73.2162	$73.22	$73.20	$73.20
Purchase #5	$250.78	11.165%	$278.7796	$278.78	$278.80	$278.80
Purchase #6	$93.53	9.825%	$102.7193	$102.72	$102.70	$102.70
Purchase #7	$110.38	13.700%	$125.5021	$125.50	$125.50	$125.50
7 purchase totals =	$906.51		$999.6031	$999.61	$999.60	$999.60