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	$53.72	6.158%	$57.0281	$57.03	$57.05	$57.00
Purchase #2	$64.39	3.447%	$66.6095	$66.61	$66.60	$66.60
Purchase #3	$248.95	7.783%	$268.3258	$268.33	$268.35	$268.30
Purchase #4	$127.38	9.401%	$139.355	$139.36	$139.35	$139.40
Purchase #5	$53.46	6.336%	$56.8472	$56.85	$56.85	$56.80
Purchase #6	$171.97	8.134%	$185.958	$185.96	$185.95	$186.00
Purchase #7	$188.71	9.635%	$206.8922	$206.89	$206.90	$206.90
7 purchase totals =	$908.58		$981.0158	$981.03	$981.05	$981.00