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	$127.66	11.671%	$142.5592	$142.56	$142.55	$142.60
Purchase #2	$78.37	4.143%	$81.6169	$81.62	$81.60	$81.60
Purchase #3	$194.76	9.282%	$212.8376	$212.84	$212.85	$212.80
Purchase #4	$57.46	8.224%	$62.1855	$62.19	$62.20	$62.20
Purchase #5	$227.39	3.721%	$235.8512	$235.85	$235.85	$235.90
Purchase #6	$131.61	6.552%	$140.2331	$140.23	$140.25	$140.20
Purchase #7	$193.40	11.658%	$215.9466	$215.95	$215.95	$215.90
7 purchase totals =	$1,010.65		$1,091.2301	$1,091.24	$1,091.25	$1,091.20