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	$82.45	10.289%	$90.9333	$90.93	$90.95	$90.90
Purchase #2	$146.88	3.130%	$151.4773	$151.48	$151.50	$151.50
Purchase #3	$84.65	9.194%	$92.4327	$92.43	$92.45	$92.40
Purchase #4	$33.81	6.387%	$35.9694	$35.97	$35.95	$36.00
Purchase #5	$236.29	6.104%	$250.7131	$250.71	$250.70	$250.70
Purchase #6	$87.42	4.684%	$91.5148	$91.51	$91.50	$91.50
Purchase #7	$224.96	12.861%	$253.8921	$253.89	$253.90	$253.90
7 purchase totals =	$896.46		$966.9327	$966.92	$966.95	$966.90