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	$56.66	7.706%	$61.0262	$61.03	$61.05	$61.00
Purchase #2	$106.78	12.293%	$119.9065	$119.91	$119.90	$119.90
Purchase #3	$53.85	13.829%	$61.2969	$61.30	$61.30	$61.30
Purchase #4	$30.99	7.591%	$33.3425	$33.34	$33.35	$33.30
Purchase #5	$142.60	3.275%	$147.2702	$147.27	$147.25	$147.30
Purchase #6	$98.61	4.335%	$102.8847	$102.88	$102.90	$102.90
Purchase #7	$65.85	11.640%	$73.5149	$73.51	$73.50	$73.50
7 purchase totals =	$555.34		$599.2419	$599.24	$599.25	$599.20