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	$75.50	6.600%	$80.483	$80.48	$80.50	$80.50
Purchase #2	$190.46	8.639%	$206.9138	$206.91	$206.90	$206.90
Purchase #3	$250.82	13.799%	$285.4307	$285.43	$285.45	$285.40
Purchase #4	$23.32	9.489%	$25.5328	$25.53	$25.55	$25.50
Purchase #5	$95.35	13.532%	$108.2528	$108.25	$108.25	$108.30
Purchase #6	$66.70	7.809%	$71.9086	$71.91	$71.90	$71.90
Purchase #7	$19.60	11.116%	$21.7787	$21.78	$21.80	$21.80
7 purchase totals =	$721.75		$800.3004	$800.29	$800.35	$800.30