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	$77.33	10.261%	$85.2648	$85.26	$85.25	$85.30
Purchase #2	$40.48	11.709%	$45.2198	$45.22	$45.20	$45.20
Purchase #3	$87.85	12.317%	$98.6705	$98.67	$98.65	$98.70
Purchase #4	$33.63	6.693%	$35.8809	$35.88	$35.90	$35.90
Purchase #5	$169.29	12.220%	$189.9772	$189.98	$190.00	$190.00
Purchase #6	$100.28	5.204%	$105.4986	$105.50	$105.50	$105.50
Purchase #7	$147.95	13.683%	$168.194	$168.19	$168.20	$168.20
7 purchase totals =	$656.81		$728.7058	$728.70	$728.70	$728.80