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	$238.46	12.714%	$268.7778	$268.78	$268.80	$268.80
Purchase #2	$51.95	4.337%	$54.2031	$54.20	$54.20	$54.20
Purchase #3	$149.31	7.751%	$160.883	$160.88	$160.90	$160.90
Purchase #4	$159.63	7.335%	$171.3389	$171.34	$171.35	$171.30
Purchase #5	$39.27	9.193%	$42.8801	$42.88	$42.90	$42.90
Purchase #6	$12.71	8.776%	$13.8254	$13.83	$13.85	$13.80
Purchase #7	$187.42	9.558%	$205.3336	$205.33	$205.35	$205.30
7 purchase totals =	$838.75		$917.2419	$917.24	$917.35	$917.20