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	$167.27	3.731%	$173.5108	$173.51	$173.50	$173.50
Purchase #2	$31.59	12.504%	$35.54	$35.54	$35.55	$35.50
Purchase #3	$37.32	4.210%	$38.8912	$38.89	$38.90	$38.90
Purchase #4	$60.76	9.557%	$66.5668	$66.57	$66.55	$66.60
Purchase #5	$170.46	9.121%	$186.0077	$186.01	$186.00	$186.00
Purchase #6	$160.91	11.644%	$179.6464	$179.65	$179.65	$179.60
Purchase #7	$84.96	4.385%	$88.6855	$88.69	$88.70	$88.70
7 purchase totals =	$713.27		$768.8484	$768.86	$768.85	$768.80